U.S. patent application number 11/872699 was filed with the patent office on 2008-10-02 for aqueous eletrodeposition of magnetic cobalt-samarium alloys.
Invention is credited to Ken Nobe.
Application Number | 20080236441 11/872699 |
Document ID | / |
Family ID | 39792088 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080236441 |
Kind Code |
A1 |
Nobe; Ken |
October 2, 2008 |
AQUEOUS ELETRODEPOSITION OF MAGNETIC COBALT-SAMARIUM ALLOYS
Abstract
Disclosed are methods and compositions for aqueous
electrodeposition of rare earth-transitiona metal alloys (e.g.,
samarium-cobalt alloys). Also disclosed are nanostructured magnetic
coatings comprising a magnetic alloy of a rare earth metal (e.g.,
samarium) and a transition metal (e.g., cobalt). This abstract is
intended as a scanning tool for purposes of searching in the
particular art and is not intended to be limiting of the present
invention.
Inventors: |
Nobe; Ken; (US) |
Correspondence
Address: |
Ballard Spahr Andrews & Ingersoll, LLP
SUITE 1000, 999 PEACHTREE STREET
ATLANTA
GA
30309-3915
US
|
Family ID: |
39792088 |
Appl. No.: |
11/872699 |
Filed: |
October 15, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60851389 |
Oct 13, 2006 |
|
|
|
60852286 |
Oct 17, 2006 |
|
|
|
Current U.S.
Class: |
106/1.05 ;
205/238 |
Current CPC
Class: |
H01F 10/126 20130101;
C25D 3/56 20130101; C25D 5/18 20130101; H01F 41/26 20130101 |
Class at
Publication: |
106/1.05 ;
205/238 |
International
Class: |
C25D 3/56 20060101
C25D003/56 |
Goverment Interests
ACKNOWLEDGEMENT
[0002] This invention was made with government support under Grant
No. DMI-0089095 awarded by the National Science Foundation. The
United States government has certain rights in the invention.
Claims
1. A composition for enhancing the aqueous electrodeposition of
rare earth-transition metal alloys comprising: a water soluble salt
of samarium, a water soluble salt of cobalt, and a complexant.
2. The composition of claim 1, wherein the water soluble salt of
samarium is samarium sulfamate.
3. The composition of claim 1, wherein the water soluble salt of
cobalt is cobalt sulfate or cobalt sulfamate.
4. The composition of claim 1, wherein the complexant is selected
from one or more amine carboxylates, one or more hydroxycarboxylic
acids, and combinations thereof.
5. The composition of claim 1, further comprising one or more
supporting electrolytes.
6. The composition of claim 5, wherein the one or more supporting
electrolytes is selected from ammonium sulfamate, ammounium
sulfate, ammonium chloride, and mixtures thereof.
7. The composition of claim 1, comprising from about 0.25M to about
2.0M of the water soluble salt of samarium, from about 0.01M to
about 0.5M of the water soluble salt of cobalt, from about 0.05M to
about 0.5M of the complexant, and from about 0M to about 3M of one
or more supporting electrolytes.
8. The composition of claim 7, comprising about 1M of the water
soluble salt of samarium, about 0.05M of the water soluble salt of
cobalt, about 0.15M of the complexant, and about 1M of the one or
more supporting electrolytes.
9. A method for electrodepositing a samarium-cobalt coating onto a
conducting substrate, comprising: a. placing an aqueous solution
containing a water soluble salt of samarium, a water soluble salt
of cobalt, one or more supporting electrolytes, and a complexant
into a plating bath, b. placing an anode and the substrate to be
coated into the bath and connecting the anode and the substrate to
a power supply, with the substrate acting as a cathode, c.
adjusting the pH of the bath to a suitable operating level, and d.
applying a current through the anode and substrate causing the
samarium and the cobalt to migrate to, and adhere to, the
substrate.
10. The method of claim 9, wherein the water soluble salt of
samarium is samarium sulfamate.
11. The method of claim 9, wherein the water soluble salt of cobalt
is cobalt sulfate or cobalt sulfamate.
12. The method of claim 9, wherein the complexant is selected from
one or more amine carboxylates, one or more hydroxycarboxylic
acids, and combinations thereof.
13. The method of claim 9, wherein the one or more supporting
electrolytes is selected from ammonium sulfamate, ammounium
sulfate, ammonium chloride, and mixtures thereof.
14. The method of claim 9, wherein the aqueous solution further
comprises boric acid.
15. The method of claim 9, wherein the aqueous solution comprises
from about 0.25M to about 2.0M of the water soluble salt of
samarium, from about 0.01M to about 0.5M of the water soluble salt
of cobalt, from about 0.05M to about 0.5M of the complexant, and
from about 0.0001M to about 3M of the supporting electrolytes.
16. The method of claim 15, wherein the aqueous solution comprises
about 1M of the water soluble salt of samarium, about 0.05M of the
water soluble salt of cobalt, about 0.15M of the complexant, and
about 1M of the supporting electrolytes.
17. The method of claim 9, wherein a current density of from about
5 mA/cm.sup.2 to about 600 mA/cm.sup.2 is applied across the anode
and cathode.
18. The method of claim 9, wherein the current is applied with
pulse current modifications varying with duty cycle and
frequency.
19. The method of claim 9, wherein the pH of the solution is from
about 4 to about 6.5.
20. The method of claim 9, wherein the solution temperature is
adjusted to from about 25.degree. C. to about 60.degree. C.
21. A samarium-cobalt coating produced by the method of claim
9.
22. A nanostructured magnetic coating comprising a magnetic alloy
of a rare earth metal and a transition metal.
23. The nanostructured magnetic coating of claim 22, wherein the
rare earth metal is samarium and wherein the transition metal is
cobalt.
24. The nanostructured magnetic coating of claim 22, wherein the
coating is provided by electrodeposition from an aqueous
solution.
25. The nanostructured magnetic coating of claim 22, wherein the
alloy comprises SmCo.sub.5 or Sm.sub.2Co.sub.17.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Application No.
60/851,389, filed Oct. 13, 2006, and U.S. Application No.
60/852,286, filed Oct. 17, 2006, which are hereby incorporated
herein by reference in their entireties.
BACKGROUND
[0003] Bulk alloys of transition metals-rare earths are important
permanent magnet materials. When using conventional techniques,
however, the current high materials and processing costs of Co--Sm
permanent magnets have limited their application to high
temperature and corrosive environments where costs are of secondary
importance. More specifically, only high cost metallurgical and
physical deposition methods are currently in use to fabricate
Co--Sm permanent magnets consisting of the intermetallics
SmCo.sub.5 and Sm.sub.2Co.sub.17.
[0004] In contrast, compositions and methods disclosed in U.S. Pat.
No. 6,306,276 established the basis for the successful
electrodeposition of rare earth-transition metal alloys from
aqueous media. Suitable operating and plating bath conditions to
obtain magnetic cobalt-samarium (Co-Sm) alloys from aqueous media
for high performance nanostructured permanent magnets, however,
have remained unknown in the art.
[0005] As current estimates of the global market for permanent
magnets exceed $5 billion, such suitable operating and plating bath
conditions to obtain magnetic cobalt-samarium (Co--Sm) alloys can
provide substantial savings in manufacturing costs and considerable
lower materials costs for nanotechnology applications, thereby
greatly expanding the global market share of high performance
Co--Sm permanent magnets fabricated by electrodeposition from
aqueous media.
SUMMARY
[0006] As embodied and broadly described herein, the invention, in
one aspect, relates to
[0007] Disclosed are compositions for enhancing the aqueous
electrodeposition of rare earth-transition metal alloys comprising
a water soluble salt of samarium, a water soluble salt of cobalt,
and a complexant.
[0008] Also disclosed are methods for electrodepositing a
samarium-cobalt coating onto a conducting (e.g., metal) substrate,
comprising placing an aqueous solution containing a water soluble
salt of samarium, a water soluble salt of cobalt, one or more
supporting electrolytes, and a complexant into a plating bath,
placing an anode and the substrate to be coated into the bath and
connecting the anode and the substrate to a power supply, with the
substrate acting as a cathode, adjusting the pH of the bath to a
suitable operating level, and applying a current through the anode
and substrate causing the samarium and the cobalt to migrate to,
and adhere to, the substrate.
[0009] Also disclosed are samarium-cobalt coatings produced by the
disclosed methods.
[0010] Also disclosed are nanostructured magnetic coatings
comprising a magnetic alloy of a rare earth metal and a transition
metal.
[0011] Unless otherwise expressly stated, it is in no way intended
that any method or aspect set forth herein be construed as
requiring that its steps be performed in a specific order.
Accordingly, where a disclosed method or system does not
specifically state that the steps are to be limited to a specific
order, it is no way intended that an order be inferred, in any
respect. This holds for any possible non-express basis for
interpretation, including matters of logic with respect to
arrangement of steps or operational flow, plain meaning derived
from grammatical organization or punctuation, or the number or type
of aspects described in the specification.
BRIEF DESCRIPTION OF THE FIGURES
[0012] The accompanying figures, which are incorporated in and
constitute a part of this specification, illustrate several aspects
and together with the description serve to explain the principles
of the invention.
[0013] FIG. 1 shows a graph illustrating maximum energy product for
permanent magnetic materials as a function of time.
[0014] FIG. 2 shows a phase diagram of the Sm--Co system.
[0015] FIG. 3 shows the Co-rich region of the Sm--Co phase
diagram.
[0016] FIG. 4 shows the hexagonal CaCu.sub.5 structure of
SmCo.sub.5 [C. Barrett and T. B. Massalski, Structure of metals,
Pergamon Press, Oxford, New York, (1980), p266].
[0017] FIG. 5 shows the rhombohedral Th.sub.2Ni.sub.17-type
structure of Sm.sub.2Co.sub.17 [R. C. O'Handley, Modern magnetic
materials, John Wiley & Son, Inc., New York, (2000), pp.
496-502].
[0018] FIG. 6 shows the pinning mechanism of Sm.sub.2Co.sub.17 [P.
Campbell, Permanent magnet materials and their application,
Cambridge University Press, New York, (1994), pp. 42-43].
[0019] FIG. 7 shows saturation magnetization, coercivity and
squareness of Co--Sm films versus atomic percent of Sm [S. A.
Bendson and J. H. Judy, IEEE Trans. Magnetics, 9, 627, (1973)].
[0020] FIG. 8 shows variation of resistivity, coercivity, and
saturation magnetization with film (33 nm) composition (left) and
SUBSTRATE temperature (right) under a background pressure of
2.times.10.sup.-7 Torr.sup.es.
[0021] FIG. 10 shows coercivity (left) and remanence ratio (right)
as a function of the Sm content for samples processed at Ar gas
pressures .box-solid.6.times.10.sup.-2, 8.times.10.sup.-2, and
.diamond-solid.1.times.10.sup.-1 Torr and a constant substrate
temperature 460.degree. C. [V. Neua and S. A. Shaheen, J. Appl.
Phys., 86, 7006, (1999)].
[0022] FIG. 11 is of graphs showing the effect of current density,
with oscillatory stirring, on the co-deposition of rare earth TM
alloyed with nickel, iron and cobalt respectively.
[0023] FIG. 12 is a graph showing the effect, with stirring, of
glycine/cobalt ratio on the deposition of the rare earth cobalt
mixture.
[0024] FIG. 13 is a graph showing the effect, with stirring, of
glycine and cobalt concentration on rare earth cobalt mixture
deposition.
[0025] FIG. 14 is a graph showing the effect, with stirring, of
pulse current duty cycle on rare earth cobalt mixture
deposition.
[0026] FIG. 15 is of graphs showing the effect of solution pH and
current density on the deposition of Nd--Ni, Nd--FE and Nd--Co,
respectively.
[0027] FIG. 16 is of graph showing the effect of solution stirring
on Ce--Ni deposits.
[0028] FIG. 17 shows an experimental flowchart of a Hull cell study
of DC and PC electrodeposition of Co--Sm alloys.
[0029] FIG. 18 shows a design of Hull cell and Hull cell panel.
[0030] FIG. 19 shows a schematic of pulse current
electrodeposition.
[0031] FIG. 20 shows a schematic of the setup for the Hull cell
electrodeposition system.
[0032] FIG. 21 shows an energy dispersive spectrum of an
electrodeposited Co--Sm alloy.
[0033] FIG. 22 shows Hull cell patterns of PC electrodeposition
from bath 1 at 60.degree. C. for different applied current of (a)
4.5 A and (b) 7 A. (T.sub.on=10 ms, duty cycle .gamma.=0.1 and
applied charge=50 C).
[0034] FIG. 23 shows Hull cell patterns of PC electrodeposition
from bath I at 25.degree. C. for applied charge/deposit area of (a)
100 C/15 cm.sup.2 and (b) 50 C/7.5 cm.sup.2. (T.sub.on=10 ms, duty
cycle .gamma.=0.1 and an applied current of 4.5 A).
[0035] FIG. 24 shows Hull cell patterns obtained from bath 1 at (a)
25.degree. C., (b) 60.degree. C. and (c) 80.degree. C.
[0036] FIG. 25 shows XRD patterns of deposits #3 obtained from bath
1 at 25.degree. C. and (a) 50 mA/cm.sup.2, metallic region; (b) 100
mA/cm.sup.2, burnt region; and (c) 500 mA/cm.sup.2, oxide/hydroxide
region.
[0037] FIG. 26 shows Sm deposit content obtained from bath 1 at 25,
60 and 80.degree. C. and various CDs.
[0038] FIG. 27 shows a setup for solution agitation in the Hull
cell.
[0039] FIG. 28 shows Hull cell patterns obtained from Bath 1 ar
25.degree. C. (a) without and (b) with agitation; at 60.degree. C.
(c) without and (d) with agitation.
[0040] FIG. 29 shows Sm deposit content obtained from bath 1
with/out agitation at 25 and 60.degree. C. and various CD.
[0041] FIG. 30 shows Hull cell patterns obtained from Bath 2 (1M Sm
sulfamate without glycine) at (a) 25.degree. C. and (c) 60.degree.
C.; from bath 3 (1M Sm sulfamate with 0.15M glycine) at (b)
25.degree. C. and (d) 60.degree. C.
[0042] FIG. 31 shows Hull cell patterns obtained from Bath 4 (0.05M
Co sulfate) at (a) 25.degree. C. and (b) 60.degree. C.; from bath 5
(0.05M Co sulfate, 0.15M glycine) at (c) 25.degree. C. and (d)
60.degree. C.
[0043] FIG. 32 shows Hull cell patterns obtained from bath 6 (1M Sm
sulfamate, 0.05M Co sulfate), bath 1 (1M Sm sulfamate, 0.05M Co
sulfate, 0.15M glycine) and bath 7 (1M Sm sulfamate, 0.05M Co
sulfate, 3M glycine) at (a)-(c) 25.degree. C. and (d)-(t)
60.degree. C.
[0044] FIG. 33 shows Sm deposit content obtained from plating baths
containing no, 0.15M and 3M glycine at various CD.
[0045] FIG. 34 shows XRD patterns of metallic deposits obtained
from bath 1 (with 0.15M glycine) at (a) 60.degree. C., 650
mA/cm.sup.2and (b) 25.degree. C., 50 mA/cm.sup.2 and from bath 6
(without glycine) at (c) 60.degree. C., 50 mA/cm.sup.2 and (d)
25.degree. C., 10 mA/cm.sup.2.
[0046] FIG. 35 shows Hull cell patterns obtained from Bath 1 (1M Sm
sulfamate, 0.05M Co sulfate, 0.15M glycine) at (a) 25.degree. C.
and (b) 60.degree. C.; from Bath 8 (1M Sm sulfamate, 0.05M Co
sulfate, 0.15M glycine, 1M NH.sub.4 sulfamate) at (c) 25.degree. C.
and (d) 60.degree. C.
[0047] FIG. 36 shows Sm deposit content obtained at 25 and
60.degree. C. from Bath 1 (1M Sm sulfamate, 0.05M Co sulfate, 0.15M
glycine) and Bath 8 (1M Sm sulfamate, 0.05M Co sulfate, 0.15M
glycine, 1M sulfamate) at various CD.
[0048] FIG. 37 shows Hull cell patterns obtained from Bath 1 at
25.degree. C. for (a) DC, (b) .gamma.=0.1, T.=10 ms and (c)
.gamma.=0.1, T.sub.on=0.05 ms; at 60.degree. C. for (d) DC, (e)
.gamma.=0.1, T.sub.on=10 ms and (f) .gamma.=0.1, T.=0.05 ms.
[0049] FIG. 38 shows Sm deposit content of deposits obtained from
Bath 1 at 25 and 60.degree. C. for PC electrodeposition of LH=0.05
and 10 ms (.gamma.=0.1) and for DC electrodeposition at various
PCD.
[0050] FIG. 39 shows Hull cell patterns obtained from Bath 1 at
25.degree. C. for .gamma.=0.1 (a) T.sub.on=0.05 ms, (b)
T.sub.on=0.1 ms, (c) T.sub.on=1 ms and (d) T.sub.on=10 ms.
[0051] FIG. 40 shows Sm deposit content of deposits obtained from
Bath 1 at 25.degree. C. and .gamma.=0.1 for T.sub.on=0.05, 0.1, 1
and 10 ms at various PCD.
[0052] FIG. 41 shows Hull cell patterns obtained from Bath 1 at
25.degree. C. for T.sub.on=0.1 ms at (a) .gamma.=0.05, (b)
.gamma.=0.075, (c) .gamma.=0.1, (d) .gamma.=0.2, (e) .gamma.=0.3
and (f) .gamma.=0.3 (DC).
[0053] FIG. 42 shows Sm deposit content obtained from Bath 1 at
25.degree. C. and T.sub.on=0.1 ms for .gamma.=0.05, 0.075, 0.1,
0.2, 0.3 and 1 (DC) at various PCD.
[0054] FIG. 43 shows dependence of deposit Sm content on current
density.
[0055] FIG. 44 shows dependence of current efficiency on current
density.
[0056] FIG. 45 shows dependence of deposit Sm content on
temperature.
[0057] FIG. 46 shows dependence of current efficiency on
temperature.
[0058] FIG. 47 shows dependence of magnetic saturation on deposit
Sm content (no NH.sub.4 sulfamate).
[0059] FIG. 48 shows dependence of coercivity on current
density.
[0060] FIG. 49 shows topography and microstructure of
electrodeposited Co--Sm alloys at current densities 100 mA/cm.sup.2
for plating baths of 60.degree. C. (a) with 1M NH.sub.4 sulfamate,
and (b) without NH.sub.4 sulfamate.
[0061] FIG. 50 shows XRD of electrodeposited Co--Sm alloys at 100
and 500 mA/cm.sup.2. S=brass substrate.
[0062] FIG. 51 shows the effect of CD on Sm content and CE of
Co--Sm alloys. 1 M Sm sulfamate, 0.05 M Co sulfate, 0.15 M.
[0063] FIG. 52 shows the effect of CD on deposit composition; pH 6,
1.2 p.m film thickness.
[0064] FIG. 53 shows structures of IG-RE-Glycine complexes (17):
(a) equilibrium of anionic, zwitterionic and cationic species; (b)
hetero-dinuclear trisglycine complex; (c) quasi-diglycine complex;
(d) quasi-triglycine complex.
[0065] FIG. 54 shows structures of Co--V (a) and Co--Fe--V (b)
biscitrate complexes.
[0066] FIG. 55 shows proposed mechanism of electrodeposition of
binary and ternary IG-V alloys.
[0067] FIG. 56 shows structure of Co--Mo (W) biscitrate
complexes.
[0068] FIG. 57 shows a proposed mechanism of electrodeposition of
IG-Mo (W) alloys.
[0069] FIG. 58 shows composite Co--W/Cr/Co--W/Cr deposit (12, 24):
(a) X500, not heat treated (HT); (b) H. T. in air, 916.degree. C.,
10 hrs (unetched); (c) H. T. in carburizing atmosphere, 916.degree.
C., 10 hrs (unetched); (d) H. T. in carburizing atmosphere,
916.degree. C., 10 hrs (etchant, hot Murakami). S=cobalt
strike.
[0070] FIG. 59 shows an experimental flowchart of parametric
studies of DC electrodeposition of Co--Sm alloys.
[0071] FIG. 60 shows a set up of DC electrodeposition.
[0072] FIG. 61 shows a setup of a RDE system.
[0073] FIG. 62 shows a schematic diagram of a VSM.
[0074] FIG. 63 shows a hysteresis loop of ED Co--Sm alloys.
[0075] FIG. 64 shows the effect of current density and solution
temperature on (a) samarium deposit content and (b) current
efficiency.
[0076] FIG. 65 shows the effect of current density and solution
temperature on normalized charges of Sm, Co and H.sub.2 in Co--Sm
alloys electrodeposition.
[0077] FIG. 66 shows (a) polarization curves at various current
densities and solution temperatures and (b) dependence of Sm
content on cathodic potential in Co--Sm electrodeposition.
[0078] FIG. 67 shows XRD patterns of deposits obtained from bath 1
(1M Sm sulfamate, 0.051M Co sulfate, 0.15M glycine, pH 6) at
25.degree. C. and various CDs).
[0079] FIG. 68 shows XRD patterns of deposits obtained from bath 1
(1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine, pH 6) at
60.degree. C. and various CDs.
[0080] FIG. 69 shows XRD patterns of deposits obtained from bath 1
(1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine, pH 6) at (a) 2
mA/cm.sup.2, (b) 25 mA/cm.sup.2 and (c) 50 mA/cm.sup.2 at various
solution temperatures.
[0081] FIG. 70 shows SEM of Co--Sm thin films obtained from bath 1
at 25.degree. C. and at (a)-(c) 2 mA/cm.sup.2, (d)-(f) 25
mA/cm.sup.2 and (g)-(i) 50 mA/cm.sup.2.
[0082] FIG. 71 shows SEM of Co--Sm thin films obtained from bath 1
at 60.degree. C. and at (a) (c) 25 mA/cm.sup.2, (d)-(f) 50
mA/cm.sup.2, (g)-(i) 100 mA/cm.sup.2, (j)-(l) 300 mA/cm.sup.2 and
(m)-(o) 500 mA/cm.sup.2.
[0083] FIG. 72 shows SEM of Co--Sm thin films obtained from bath 1
at 50 mA/cm.sup.2 and at (a)-(b): 25.degree. C., (c)-(d) 40.degree.
C. and (e)-(f) 60.degree. C.
[0084] FIG. 73 shows SEM of Co--Sm thin films obtained from bath 1
at 50 mA/cm.sup.2 and at (a)-(c) 25.degree. C., (d)-(f) 40.degree.
C. and (g)-(i) 60.degree. C.
[0085] FIG. 74 shows dependence of particle size on Sm deposit
content at various temperatures and CDs.
[0086] FIG. 75 shows magnetic hysteresis loops obtained at (a)-(c)
25.degree. C. and (d)-(i) 60.degree. C. and at various CDs from
bath 1.
[0087] FIG. 76 shows effects of current density and temperature on
deposit crystalline structures, particle sizes and magnetic
properties.
[0088] FIG. 77 shows the effect of the particle size on
coercivities of fiber-shaped microstructures in Co--Sm alloys.
[0089] FIG. 78 shows effect of solution pH on (a) Sm deposit
content and (b) current efficiency at 25, 60.degree. C. and various
CDs.
[0090] FIG. 79 shows XRD patterns of deposits obtained at 10
mA/cm.sup.2, 25.degree. C. and various solution pHs. (Bath: 1M Sm
sulfamate, 0.05M Co sulfate, 0.15M glycine).
[0091] FIG. 80 shows XRD patterns of deposits obtained at 50
mA/cm.sup.2, 25.degree. C. and various solution pHs. (Bath: 1M Sm
sulfamate, 0.05M Co sulfate, 0.15M glycine).
[0092] FIG. 81 shows XRD patterns of deposits obtained at 10
mA/cm.sup.2, 60.degree. C. and various solution pHs. (Bath: 1M Sm
sulfamate, 0.05M Co sulfate, 0.15M glycine).
[0093] FIG. 82 shows XRD patterns of deposits obtained at 50
mA/cm.sup.2, 60.degree. C. and various solution plls. (Bath: 1M Sm
sulfamate, 0.05M Co sulfate, 0.15M glycine).
[0094] FIG. 83 shows XRD patterns of deposits obtained at 100
mA/cm.sup.2, 60.degree. C. and various solution pHs. (Bath: 1M Sm
sulfamate, 0.05M Co sulfate, 0.15M glycine).
[0095] FIG. 84 shows XRD patterns of deposits obtained at 300
mA/cm.sup.2, 60.degree. C. and various solution pHs. (Bath: 1M Sm
sulfamate, 0.05M Co sulfate, 0.15M glycine).
[0096] FIG. 85 shows low magnitude (2,000.times.) SEM of Co--Sm
thin films obtained at (a)-(c) pH 6, (d)-(f) pH 4 and (g)-(i) pH 2
at 25.degree. C. and various CDs. (Bath: 1M Sm sulfamate, 0.05M Co
sulfate, 0.15M glycine)
[0097] FIG. 86 shows high magnitude (50,000.times.) SEM of Co--Sm
thin films obtained at (a)-(c) pH 6, (d)-(f) pH 4 and (g)-(i) pH 2
at 25.degree. C. and various CDs. (Bath: 1M Sm sulfamate, 0.05M Co
sulfate, 0.15M glycine).
[0098] FIG. 87 shows low magnitude (2,000.times.) SEM of Co--Sm
thin films at (a)-(c) pH 6, (d)-(f) pH 4 and (g)-(i) pH 2 at
60.degree. C. and various CDs. (Bath: 1M Sm sulfamate, 0.05M Co
sulfate, 0.15M glycine).
[0099] FIG. 88 shows high magnitude (50,000.times.) SEM of Co--Sm
thin films obtained at (a)-(c) pH 6, (d)-(f) pH 4 and (g)-(i) pH 2
at 60.degree. C. and various CDs. (Bath: 1M Sm sulfamate, 0.05M Co
sulfate, 0.15M glycine).
[0100] FIG. 89 shows dependence of particle size on Sm deposit
content at various pHs, temperatures and CDs.
[0101] FIG. 90 shows magnetic properties of deposits obtained at
25, 60.degree. C. and various pHs. (Bath: 1M Sm sulfamate, 0.05M Co
sulfate, 0.15M glycine).
[0102] FIG. 91 shows the effect of rotating rate of RDE on (a)
samarium deposit content and (b) current efficiency at 25.degree.
C. (Deposits of 0 rpm rotation rate were obtained from parallel
electrode because poor deposits were obtained by RDE at 0
rpm.).
[0103] FIG. 92 shows the effect of rotating rate of RDE on
normalized charges of Sm, Co and H.sub.2 in Co--Sm alloys
electrodeposition. (Deposits of 0 rpm rotation rate were obtained
from parallel electrode because poor deposits were obtained by RDE
at 0 rpm.).
[0104] FIG. 93 shows SEM of Co--Sm thin films obtained from bath 1
at 100 mA/cm.sup.2, 25.degree. C. and (a)-(c): no-agitation
(non-metallic, obtained from parallel electrode), (d)-(f) 1000 rpm
(Sm=12.5 at %), and (g)-(i) 200 rpm (Sm=7.2 at %).
[0105] FIG. 94 shows magnetic properties of deposits obtained at
25.degree. C. and various rotating rates.
[0106] FIG. 95 shows the effect of Sm sulfamate concentration on
(a) samarium deposit content and (b) current efficiency at 25 and
60.degree. C.
[0107] FIG. 96 shows the effect of Sm sulfamate concentration on
normalized charges of Sm, Co and H.sub.2 in Co--Sm alloy
electrodeposition.
[0108] FIG. 97 shows XRD patterns of deposits obtained at
25.degree. C., 25 mA/cm.sup.2 and various Sm sulfamate
concentrations. (Bath: 0.05M Co sulfate, 0.15M glycine, Sm
sulfamate varied from 0.25 to 1M, pH 6).
[0109] FIG. 98 shows XRD patterns of deposits obtained at
25.degree. C., 50 mA/cm.sup.2 and various Sm sulfamate
concentrations. (Bath: 0.05M Co sulfate, 0.15M glycine, Sm
sulfamate varied from 0.25 to 1M, pH 6).
[0110] FIG. 99 shows XRD patterns of deposits obtained at
60.degree. C., 50 mA/cm.sup.2 and various Sm sulfamate
concentrations. (Bath: 0.05M Co sulfate, 0.15M glycine, Sm
sulfamate varied from 0.25 to 1M, pH 6).
[0111] FIG. 100 shows XRD patterns of deposits obtained at
60.degree. C., 100 mA/cm.sup.2 and various Sm sulfamate
concentrations. (Bath: 0.05M Co sulfate, 0.15M glycine, 0.25 to 1M
Sm sulfamate, pH 6).
[0112] FIG. 101 shows the effect of Sm sulfamate concentration on
magnetic properties of deposits obtained at 25 and 60.degree. C.
(Bath: 0.05M Co sulfate, 0.15M glycine, Sm sulfamate varied from
0.25 to 1M, pH 6).
[0113] FIG. 102 shows the effect of glycine concentration on (a)
samarium deposit content and (b) current efficiency at 25 and
60.degree. C.
[0114] FIG. 103 shows XRD patterns of deposits obtained at
25.degree. C., 50 mA/cm.sup.2 and various glycine concentrations.
(Bath: 1M Sm sulfamate, 0.05M cobalt sulfate, glycine varied from 0
to 0.5M, pH 6).
[0115] FIG. 104 shows XRD patterns of deposits obtained at
60.degree. C., 50 mA/cm.sup.2 various glycine concentrations.
(Bath: 1M Sm sulfamate, 0.05M cobalt sulfate, glycine varied from 0
to 0.5M, pH 6).
[0116] FIG. 105 shows the effect of glycine concentration on
magnetic properties of electrodeposited Co--Sm thin films obtained
at 25 and 60.degree. C.
[0117] FIG. 106 shows the effect of NH.sub.4 sulfamate
concentration on (a) samarium deposit content and (b)
currentefficiency at 25 and 60.degree. C.
[0118] FIG. 107 shows the effect of NH.sub.4 sulfamate
concentration on normalized charges of Sm, Co and H.sub.2 in Co--Sm
alloy electrodeposition.
[0119] FIG. 108 shows XRD patterns of deposits obtained from (a)
bath 8 (1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine, 1M
NH.sub.4 sulfamate, pH 5.2) and (b) bath 1 (1M Sm sulfamate, 0.05M
Co sulfate, 0.15M glycine, pH 5.7) at 25.degree. C. and various
CDs.
[0120] FIG. 109 shows XRD patterns of deposits obtained from (a)
bath 8 (1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine, 1M
NH.sub.4 sulfamate, pH 5.2) and (b) bath 1 (1M Sm sulfamate, 0.05M
Co sulfate, 0.15M glycine, pH 5.7) at 60.degree. C. and various
CDs.
[0121] FIG. 110 shows SEM (2,000.times.) of Co--Sm thin films from
bath (a)-(b) without (bath 1) and (c)-(d) with 1M NH.sub.4
sulfamate (bath 8).
[0122] FIG. 111 shows SEM (50,000.times.) of Co--Sm thin films from
bath (a)-(c) without (bath 1) and (d)-(l) with 1M NH.sub.4
sulfamate (bath 8).
[0123] FIG. 112 shows the effect of NH.sub.4 sulfamate
concentration on magnetic properties of electrodeposited Co--Sm
thin films obtained at 25 and 60.degree. C. (Bath: 1M Sm sulfamate,
0.05M Co sulfate, 0.15M glycine, NH.sub.4 sulfamate varied from 0
to 1M).
[0124] FIG. 113 shows the effect of supporting electrolyte on
samarium deposit at (a) 25 and (b) 60.degree. C.
[0125] FIG. 114 shows the effect of supporting electrolyte on
current efficiency at (a) 25 and (b) 60.degree. C.
[0126] FIG. 115 shows the effect of supporting electrolyte on
normalized charge of Sm, Co and H.sub.2 at 25.degree. C. and
60.degree. C. in Co--Sm electrodeposition.
[0127] FIG. 116 shows SEM of Co--Sm thin films obtained from bath
with (a)-(c) no supporting electrolyte, (d)-(f) 1M NH.sub.4
sulfamate, (g)-(i) 1M NH.sub.4Cl and (j)-(l) 1M KCl at 25.degree.
C. and 25 mA/cm.sup.2. (Bath: 1M Sm sulfamate, 0.05M Co sulfate,
0.15M glycine with different types of supporting electrolytes)
60.degree. C., 300 mA/cm.sup.2.
[0128] FIG. 117 shows SEM of Co--Sm thin films obtained from bath
with (a)-(c) no supporting electrolyte, (d)-(0.1M NH.sub.4
sulfamate, (g)-(i) 1M NH.sub.4C1 and (j)-(l) 1M KCl at 60.degree.
C. and 300 mA/cm.sup.2. (Bath: 1M Sm sulfamate, 0.05M Co sulfate,
0.15M glycine with different types of supporting electrolytes).
[0129] FIG. 118 shows the effect of types of supporting
electrolytes on magnetic properties of electrodeposited Co--Sm thin
films obtained at 25 and 60.degree. C. (Bath: 1M Sm sulfamate,
0.05M Co sulfate, 0.15M glycine with different types of supporting
electrolytes).
[0130] FIG. 119 shows dependence of Bragg angle (2%) of (10.0) and
(00.2) planes on Sm deposit content obtained at 60.degree. C.
[0131] FIG. 120 shows an experimental flowchart of parametric
studies of PC electrodeposition of Co--Sm alloys.
[0132] FIG. 121 shows a schematic of pulse current
electrodeposition.
[0133] FIG. 122 shows a setup for PC electrodeposition.
[0134] FIG. 123 shows the effect of peak current density and
solution temperature on (a) samarium deposit content and (b)
current efficiency for DC and PC (T.sub.on=0.1 ms, .gamma.=0.1)
electrodeposition.
[0135] FIG. 124 shows the effect of peak current density and
solution temperature on normalized charges of Sm, Co and I-1.sub.2
in Co--Sm alloys electrodeposition by DC and PC (T.sub.on=0.1 ms,
.gamma.=0.1) electrodeposition.
[0136] FIG. 125 shows XRD patterns of deposits obtained from bath 1
(1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine, pH 6) at 25 and
60.degree. C. and various PCDs.
[0137] FIG. 126 shows SEM of Co--Sm thin films obtained from bath 1
at 25.degree. C. and various PCDs.
[0138] FIG. 127 shows SEM of Co--Sm thin films obtained from bath 1
at 60.degree. C. and various PCDs.
[0139] FIG. 128 shows magnetic hysteresis loops obtained at (a)-(c)
25.degree. C. and (d)-(i) 60.degree. C. and at various PCDs from
bath 1.
[0140] FIG. 129 shows effects of peak current density and
temperature on magnetic properties.
[0141] FIG. 130 shows the effect of duty cycle on (a) samarium
deposit content and (b) current efficiency (T.sub.on=0.1 ms).
[0142] FIG. 131 shows the effect of duty cycle on normalized
charges of Sm, Co and H.sub.2, in Co--Sm alloys electrodeposition
(T.sub.on=0.1 ms, .gamma.=0.1).
[0143] FIG. 132 shows XRD patterns of deposits obtained from bath 1
(1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine, pH 6) at 25 and
60.degree. C., 500 mA/cm.sup.2 and various duty cycles.
[0144] FIG. 133 shows SEM of Co--Sm thin films obtained from bath 1
at 25 and 60.degree. C., 500 mA/cm.sup.2, and various duty
cycles.
[0145] FIG. 134 shows the effects of duty cycles on magnetic
properties.
[0146] FIG. 135 shows the effect of frequency on (a) samarium
deposit content and (b) current efficiency (.gamma.=0.1, 25.degree.
C.).
[0147] FIG. 136 shows the effect of frequency on normalized charges
of Sm, Co and H.sub.2 in Co--Sm alloys electrodeposition
(.gamma.=0.1, 25.degree. C.).
[0148] FIG. 137 shows XRD (left) and SEM (right) of deposits
obtained from bath 1 at various frequencies (100 mA/cm.sup.2,
.gamma.=0.1, 25.degree. C.).
[0149] FIG. 138 shows SEM of Co--Sm thin films obtained from bath 1
at 25.degree. C., 2 kHz, .gamma.=0.1 and at (a)-(b) 500 mA/cm.sup.2
and (c)-(d) 500 mA/cm.sup.2.
[0150] FIG. 139 shows the effects of frequency on magnetic
properties at 25.degree. C.
[0151] FIG. 140 shows the effect of T.sub.on on (a) samarium
deposit content and (b) current efficiency (period=100 ms,
25.degree. C.).
[0152] FIG. 141 shows the effect of T.sub.on on normalized charges
of Sm, Co and H.sub.2 in Co--Sm alloys electrodeposition
(period=100 ms, 25.degree. C.).
[0153] FIG. 142 shows XRD (left) and SEM (right) of deposits
obtained from bath 1 at various T.sub.on (1000 mA/cm.sup.2,
period=1000 ms, 25.degree. C.).
[0154] FIG. 143 shows the effects of T.sub.on on magnetic
properties.
[0155] FIG. 144 shows Deposition rates of Sm and Co vs. deposition
time in the electrodeposition of Co--Sm alloys.
[0156] Additional advantages of the invention will be set forth in
part in the description which follows, and in part will be obvious
from the description, or can be learned by practice of the
invention. The advantages of the invention will be realized and
attained by means of the elements and combinations particularly
pointed out in the appended claims. It is to be understood that
both the foregoing general description and the following detailed
description are exemplary and explanatory only and are not
restrictive of the invention, as claimed.
DETAILED DESCRIPTION
[0157] The present invention can be understood more readily by
reference to the following detailed description of the invention
and the Examples included therein.
[0158] Before the present compounds, compositions, articles,
systems, devices, and/or methods are disclosed and described, it is
to be understood that they are not limited to specific synthetic
methods unless otherwise specified, or to particular reagents
unless otherwise specified, as such may, of course, vary. It is
also to be understood that the terminology used herein is for the
purpose of describing particular aspects only and is not intended
to be limiting. Although any methods and materials similar or
equivalent to those described herein can be used in the practice or
testing of the present invention, example methods and materials are
now described.
[0159] All publications mentioned herein are incorporated herein by
reference to disclose and describe the methods and/or materials in
connection with which the publications are cited. The publications
discussed herein are provided solely for their disclosure prior to
the filing date of the present application. Nothing herein is to be
construed as an admission that the present invention is not
entitled to antedate such publication by virtue of prior invention.
Further, the dates of publication provided herein can be different
from the actual publication dates, which may need to be
independently confirmed.
A. Definitions
[0160] As used in the specification and the appended claims, the
singular forms "a," "an" and "the" include plural referents unless
the context clearly dictates otherwise. Thus, for example,
reference to "a substrate," "an alloy," or "a sample" includes
mixtures of two or more such substrates, alloys, or samples, and
the like.
[0161] Ranges can be expressed herein as from "about" one
particular value, and/or to "about" another particular value. When
such a range is expressed, another aspect includes from the one
particular value and/or to the other particular value. Similarly,
when values are expressed as approximations, by use of the
antecedent "about," it will be understood that the particular value
forms another aspect. It will be further understood that the
endpoints of each of the ranges are significant both in relation to
the other endpoint, and independently of the other endpoint. It is
also understood that there are a number of values disclosed herein,
and that each value is also herein disclosed as "about" that
particular value in addition to the value itself. For example, if
the value "10" is disclosed, then "about 10" is also disclosed. It
is also understood that each unit between two particular units are
also disclosed. For example, if 10 and 15 are disclosed, then 11,
12, 13, and 14 are also disclosed.
[0162] As used herein, the terms "optional" or "optionally" means
that the subsequently described event or circumstance may or may
not occur, and that the description includes instances where the
event or circumstance occurs and instances where it does not.
[0163] Disclosed are the components to be used to prepare the
compositions of the invention as well as the compositions
themselves to be used within the methods disclosed herein. These
and other materials are disclosed herein, and it is understood that
when combinations, subsets, interactions, groups, etc., of these
materials are disclosed that while specific reference of each
various individual and collective combinations and permutation of
these compounds may not be explicitly disclosed, each is
specifically contemplated and described herein. For example, if a
particular compound is disclosed and discussed and a number of
modifications that can be made to a number of molecules including
the compounds are discussed, specifically contemplated is each and
every combination and permutation of the compound and the
modifications that are possible unless specifically indicated to
the contrary. Thus, if a class of molecules A, B, and C are
disclosed as well as a class of molecules D, E, and F and an
example of a combination molecule, A-D is disclosed, then even if
each is not individually recited each is individually and
collectively contemplated meaning combinations, A-E, A-F, B-D, B-E,
B-F, C-D, C-E, and C-F are considered disclosed. Likewise, any
subset or combination of these is also disclosed. Thus, for
example, the sub-group of A-E, B-F, and C-E would be considered
disclosed. This concept applies to all aspects of this application
including, but not limited to, steps in methods of making and using
the compositions of the invention. Thus, if there are a variety of
additional steps that can be performed it is understood that each
of these additional steps can be performed with any specific aspect
or combination of aspects of the methods of the invention.
[0164] It is understood that the compositions disclosed herein have
certain functions. Disclosed herein are certain structural
requirements for performing the disclosed functions, and it is
understood that there are a variety of structures that can perform
the same function that are related to the disclosed structures, and
that these structures will typically achieve the same result.
B. Rare Earth-Transition Metal (RE-TM) Permanent Magnets
[0165] RE-TM permanent magnets were developed at 1960's and became
a practical commercial product at 1970. At that time, the RE-TM
permanent magnets offered ten times higher coercivity and five
times greater energy density than the best magnets of the 1960's.
The maximum energy product for hard permanent magnetic materials is
shown in FIG. 1 [G. J. Long and F. Grandjean, Supermagnets, hard
magnetic materials, Kluwer Academic Publishers, Norwell, Mass.,
(1991), p3.].
[0166] RE-TM permanent magnets of different compositions exhibit a
wide range of magnetic properties and cost; the research and
development of Sm--Co and Nd--Fe-B alloys got more attention among
these magnets for their superior performance and practical
applications [K. J. Stmat, IEEE Trans. Magnetics, Mag-23, 2094,
(1987).]. The first practical RE-TM permanent magnet, sintered
SmCo.sub.5, was available about 1970 in the U.S. [M. G. Benz and D.
L. Martin, Appl. Phys. Letters, 17, 176, (1970).]. Right after
SmCo.sub.5, the investigation of quasi-binary intermetallics,
RE.sub.2(Co, Fe).sub.17 [A. E. Ray and K. J. Strnat, IEEE Trans.
Magnetics, Mag-8, 516, (1972); K. J. Strnat, IEEE Trans. Magnetics,
Mag-8, 511, (1972).], led to the development of the second
generation of REIG permanent magnet --Sm.sub.2Co.sub.17. The first
useful Sin.sub.2Co.sub.17 was developed in Japan in 1975 [T. Ojima,
S. Tomizawa, T. Yoneyama, and T. Hori, Japan. J. Appl. Phys., 16,
671, (1977).]. The third generation of RE-TM permanent magnets,
Nd.sub.2Fel.sub.4B, was developed by US and Japanese researchers
and announced in 1983 [7; J. J. Croat, J. F. Herbst, R. W. Lee and
F. E. Pinkerton, J. Appl. Phys., 55, 2078, (1984); N. C. Koon and
B. N. Das, J. Appl. Phys., 55, 2063, (1984).] and brought new, much
higher energy-product permanent magnets and a promise for cheaper
RE-TM permanent magnets. The development of RE-TM permanent magnets
not only resulted in a breakthrough of high performance magnetic
materials but also created new applications for ferromagnetism
materials.
[0167] Driven by the increasing interest of high performance
permanent magnets, the improvement of RE-TM magnets has been mainly
done by the incorporation and substitution of specific elements to
RE-TM alloys. For example, small substitution of Cu for Co in
SmCo.sub.5 leads to the precipitation of a nonmagnetic phase which
increased the coercivity [E. A. Nesbitt, R. H. Willens, R. C.
Sherwood, E. Buehler, and J. H. Wernick, Appl. Phys. Letters, 12,
361, (1968).]; the replacement of parts of Co by Fe in
Sm.sub.2Co.sub.17 resulted in greater magnetization saturation (Ms)
[A. E. Ray and K. J. Strnat, IEEE Trans. Magnetics, Mag-8, 516,
(1972).] the replacement of 50% of Fe by Co in Nd.sub.2Fe.sub.14B
gives higher Curie temperature [R. Grossinger, R. Krewenka, H.
Buchner, and H. Harada, J. Phys. (Paris), 49, C8-659, (1988).].
These improvements make RE-TM permanent magnets easier to use for
different kinds of industrial applications (Table 1) and enhances
the performance of these magnetic devices.
[0168] Except for the traditional ways of making RE-TM magnets
(i.e., bonding and sintering [M. G. Benz and D. L. Martin, Appl.
Phys. Letters, 17, 176, (1970); M. G. Benz and D. L. Martin, J.
Appl. Phys., 43, 4733, (1972); A. E. Ray and K. J. Strnat, IEEE
Trans. Magnetics, Mag-11, 1429, (1975).]), new manufacture methods
(i.e. mechanical alloying [J. Wecker, M. Katter and L. Schultz, J.
Appl. Phys., 69, 6085, (1991); J. Ding, P. G. McCormick and R.
Street, J. Alloys Comp., 191, 197, (1993).], nano powder metallurgy
[J. Ding, Y. Liu, P. G. McCormick and R. Street, J. Magn. Magn.
Mater., 123, L239, (1993).], and thin film processes -DC sputtering
[H. C. Theuerer, E. A. Nesbitt, and D. D. Bacon, J. Appl. Phys.,
40, 2994, (1969); S. A. Bendson and J. H. Judy, IEEE Trans.
Magnetics, 9, 627, (1973); C. Zhang, R. Liu and G. Feng, IEEE
Trans. Magnetics, 16, 1215, (1980); H. S. Cho, J. R. Salem, A. J.
Kellock and R. B. Beyers, IEEE Trans. Magnetics, 33, 2890, (1997);
R. Andreescu and M. J. O'Shea, I Appl. Phys., 91, 8183, (2002);
22], Rf sputtering [V. Neua and S. A. Shaheen, J. Appl. Phys., 53,
2401, (1982); F. J. Cadieu, S. H. Aly and T. D. Cheung, J. Appl.
Phys., 64, 5501, (1988); K. Chen, H. Hegde and F. J. Cadieu, Appl.
Phys. Letters, 61, 1861, (1992); T. Numata, H. Kinyama and S.
Inokuchi, Appl. Phys., 86, 7006, (1999).], PVD [V. Geiss, E.
Kneller and A. Nest, Appl. Phys., A27, 79, (1982); M. Gronau, H.
Goeke, D. Schaffler and S. Sprenger, IEEE Trans. Magnetics, Mag-19,
1653, (1983); U. Kullmann, E. Koester and C. Dorsch, IEEE Trans.
Magnetics, Mag-20, 420, (1984).], and pulsed laser deposition [V.
Neu, J. Thomas, S. Faller, B. Holzapfel and L. Schultz, J. Magn.
Magn. Mater., 242-245, 1290, (2002); F. J. Cadieu, R. Rani, and T.
Theodoropoulos and Li Chen, J. Appl. Phys., 85, 5895, (1999).])
have been studied and developed. The improvement of manufacturing
process not only promotes these high performance devices for
traditional applications (i.e., automotive, domestic, electronic,
aerospace devices) but also for new industrial applications, such
as information storage, micro-electromechanical systems (MEMS), and
nano-electromechanical systems (NEMS) of thin film RE-TM
magnets.
TABLE-US-00001 TABLE 1 Applications of permanent magnets
Application Magnetic Devices and Products Automotive dc motor
drivers, starter motors, window winders, wipers, fans, speed
meters, alternators Domestic analogues, watches, video recorders,
electric clocks, hearing aids, loudspeakers Electronic and sensors,
contactless switches, nmr spectrometers, energy meter
Instrumentation bearing, transducers, computer printer head, damper
Aerospace frictionless bearings, couplings, magnetrons, klystrons,
auto compasses Biosurgical dentures, magnetic sphincters, magnetic
sutures, cancer cell separators, artifical hearts Information
storage magneto-optical recording medium, perpendicular recording
media, MEMS & NEMS micromotor, actuator, magnetometer, magnetic
sensors, magnetic bubble memory
[0169] Recent developments of RE-TM magnets have focused on Co--Sm
thin films by sputtering on the substrate with Cr underlayer [C.
Prados and G. C. Hadjipanayis, J Appl. Phys., 83, 6253, (1998); C.
Prados, A. Hernando, G. C. Hadjipanayis and J. M. Gonza'leza, J.
Appl. Phys., 85, 6148, (1999); C. Prados and G. C. Hadjipanayis,
Appl. Phys. Letters, 74, 430, (1999).]. Proper deposition
conditions, alloy composition, and heat treatments increase the
coercivity up to 40 kOe which is much higher than the coercivity of
conventional SmCo.sub.5 (about 10 kOe) by other processes. In
addition, using Cu as under layer in the sputtering process changes
Co--Sm alloys from an in-plane to a perpendicular magnetic
anisotropy [J Sayama, T. Asahi, K. Mizutani and T. Osaka, J. Phys.
D: Appl. Phys., 37, L1, (2004); J. Sayama, K. Mizutani, T. Asahi,
J. Ariake, K. Ouchi, S. Matsunuma and T. Osaka, J. Magn. Magn.
Mater., 287, 239, (2005).], which makes it a good candidate for
high density perpendicular recording media (also in terms of its
excellent thermal stability and small minimal stable grain
size).
[0170] A disadvantage of RE-TM permanent magnets to complete in the
world market and wide use is their price [G. J. Long and F.
Grandjean, Supermagnets, hard magnetic materials, Kluwer Academic
Publishers, Norwell, Mass., (1991), pp 585-616.] which is strongly
dependent on the manufacture process. Thin film processes, such as
sputtering, PVD, and pulsed laser deposition, require a vacuum
system and a high purity target to avoid impurity in deposits. In
addition, the growth rates of these processes are slow. Therefore,
making Co--Sm thin films by these processes is quite expensive and
cannot provide any advantage in cost reduction making it difficult
for commercialization. In other words, a cost effective
manufacturing method must be developed to reduce the fabrication
cost.
[0171] Electrodeposition is a simple, versatile and
easily-controlled thin/thick film manufacturing method because of
its simple setup, easy maintenance, low temperature operation, and
low energy consumption. Compared to sputter, PVD, and other thin
film processes, the most important advantage of electrodeposition
is low cost. It was indicated that PVD process may be as much as
ten times more expensive than electrodeposition [J. W. Dini, Plat.
Surf: Finish., 80, 26, (1993).]. In addition, the growth rate of
electrodeposition (5-0.1 .mu.m/min) is a lot faster than other thin
film processes (0.1-0.001 .mu.m/min). This gives electrodeposition
an advantage over other "thin film" technologies in thick film
deposition which is often required in MEMS devices. With the help
of masking patterns formed on the seedlayer, deposits of complex
shape and geometry can be obtained by the electrodeposition.
Therefore, electrodeposition is especially suitable to achieve high
aspect ratio devices and microstructures in LIGA process [A. E. Ray
and K. J. Strnat, IEEE Trans. Magnetics, Mag-8, 516, (1972).]. This
provides electrodeposition more versatility and variety making it
capable to adapt to various kind of applications. Therefore, using
electrodeposition should effectively reduce the fabrication cost of
RE-TM thin films and make them more competitive compared to other
thin film technologies RE metal and alloys have been
electrodeposited from molten salts [T. Iida T. Nohira and Y. Ito,
Electrochim. Acta, 48, 901, (2003); T. Iida T. Nohira and Y. Ito,
Electrochim. Acta, 48, 901, (2003).[P. Liu, Y. Du, Q. Yang, Y. Tong
and G. A. Hope, J. Magn. Magn. Mater., 153, C57, (2006).] and
nonaqueous solutions [Y. Sato, H. Ishida, K. Kobayakawa and Y. Abe,
Chem. Lett., (8), 1471, (1990); Y. Sato, T. Takazawa, M. Takahashi,
H. Ishida and K. Kobayakawa, Plat. Surf Finish., 80, 72, (1993).].
Unfortunately, most of the deposits obtained from non-aqueous media
have poor magnetic properties, as low coercivity and saturation
magnetization; oxides and hydroxides also be found in some cases
after heat treatments [Y. Sato, T. Takazawa, M. Takahashi, H.
Ishida and K. Kobayakawa, Plat. Surf Finish., 80, 72, (1993).]. On
the other hand, few studies of the electrodeposition of IG-RE
alloys from aqueous solutions have been reported [L. Chen, M.
Schwartz, and K. Nobe, in Electrodeposited Thin Films, M. Paunovic
and D. A. Scherson, Editors, PV 96-19, p. 239, The Electrochemical
Society Proceedings Series, Pennington, N.J. (1996); Schwartz et
al., in Magnetic Materials, Processes, and Devices V. Applications
to Storage and Microelectromechanical Systems (MEMS), Romankiw et
al., Editors, PV 98-20, p. 646, The Electrochemical Society
Proceedings Series, Pennington, N.J. (1999); M. Schwartz, N. V.
Myung, and K. Nobe, J. Electrochem. Soc., 151, C468, (2004).].
[0172] Electrodeposition of RE metals from aqueous solutions is
more difficult compared to non-aqueous solutions, as a result of
anticipated vigorous hydrogen evolution at the reduction potentials
of RE metals in aqueous solution. The reduction potentials of RE
metals are extremely negative (E.degree.<-2VsitE) [W. M.
Latimer, The Oxidation States of the Elements and Their Potentials
in Aqueous Solution, Prentice-Hall, New York, pp. 286-295
(1952).],muchlowerthanthereductionpotentialofwater
(H.sub.2O+2e.sup.-20H.sup.-+1/2H.sub.2, E-0.826V). Therefore,
instead of RE metal deposition, water can decompose first. In
addition, RE metal ions would be hydrolyzed at PH>6 and tends to
react with dissolved oxygen or hydroxyl ions to form oxide or
hydroxide. Therefore, hydroxides and oxides would be deposited
instead of RE metal making the deposition of RE metal from aqueous
solution difficult, similar to electrodeposition of Mo, W and V
from aqueous solutions. However, Mo, W and V has been
co-electrodeposited with iron group metals from aqueous solution
the addition [L. O. Case and A. Krohn, J. Electrochem. Soc., 105,
512 (1958); V. B. Singh, L. C. Singh, and P. K. Tikoo, J.
Electrochem. Soc., 127, 590 (1980); M. Schwartz, Unpublished data,
1946; see also discussion in Trans. Electrochem. Soc., 94, 382
(1948); A. Brenner, P. Burkhead, and E. Seegmiller, J. Res. Natl.
Bur. Stand., 93, 351 (1947); M. L. Holt and L. E. Vaaler, Trans.
Electrochem. Soc., 94, 50 (1948);W. E. Clark and M. L. Holt, Trans.
Electrochem. Soc., 94, 244 (1948); M. H. Lietzke and M. L. Holt,
Trans. Electrochem. Soc., 94, 252 (1948); W. H. Safranek and L. E.
Vaaler, Plating (East Orange, N.J.), 46, 133 (1959); Arcos et al.,
Magnetic Materials, Processes, and Devices IV. Applications to
Storage and Microelectromechanical Systems (MEMS), Romankiw and
Herman, Jr., Editors, PV 95-18, p. 563, The Electrochemical
Proceedings Series, Pennington, N.J. (1996); Arcos et al., Plat.
Surf Finish., 90 46 (2003).] of an appropriate complexer. Various
hypotheses has been reviewed by Brenner [A. Brenner,
Electrodeposition of Alloys, Vol. 2, pp. 400-453, Academic Press,
NewYork (1963).] to explain the phenomenon of the co-reduction of
these metals, which he referred to as "induced" co-deposition.
[0173] In 1947-1948, Schwartz initiated a commercial installation
of a Co-W ammonium citrate plating process [J Sayama, T. Asahi, K.
Mizutani and T. Osaka, J. Phys. D: Appl. Phys., 37, L1, (2004).].
He found that when solutions of Co and W salt were mixed, cobalt
tungstate precipitate immediately but dissolved with the addition
of citrate. He conjectured that both Co.sup.2+ and W.sup.6+ are
present in the same complex with deportonation of the
hydroxycarboxylate portions, resulting in a heteronuclear
biscitrate complex.
[0174] In 1994, Schwartz initial research of the electrodeposition
of IG-RE alloys from aqueous solution [M. Schwartz, Unpublished
data, UCLA 1994] and tried to extend his idea of complex formation
in aqueous Co--W alloy electrodeposition to IG-RE alloys. Between
1996 and 2004, a series of studies of IG-RE alloys from aqueous
solutions were reported [L. Chen, M. Schwartz, and K. Nobe, in
Electrodeposited Thin Films, M. Paunovic and D. A. Scherson,
Editors, PV 96-19, p. 239, The Electrochemical Society Proceedings
Series, Pennington, N.J. (1996); Schwartz et al., in Magnetic
Materials, Processes, and Devices V. Applications to Storage and
Microelectromechanical Systems (MEMS), Romankiw et al., Editors, PV
98-20, p. 646, The Electrochemical Society Proceedings Series,
Pennington, N.J. (1999); M. Schwartz, N. V. Myung, and K. Nobe, J.
Electrochem. Soc., 151, C468, (2004); Myung et al., in Fundamental
Aspects of Electrochemical Deposition and Dissolution, Matlosz et
al., Editors, PV 99-33, p. 263, The Electrochemical Society
Proceedings Series, Pennington, N.J. (1999).]. The experimental
results indicated that RE and IG metals can be co-deposited by
addition of appropriate complexes, such as glycine and its
derivatives, into the solution. Initially, studies were mainly
focused on RE mixtures [L. Chen, M. Schwartz, and K. Nobe, in
Electrodeposited Thin Films, M. Paunovic and D. A. Scherson,
Editors, PV 96-19, p. 239, The Electrochemical Society Proceedings
Series, Pennington, N.J. (1996).] for co-deposition of IG-RE alloys
[Schwartz et al., in Magnetic Materials, Processes, and Devices V.
Applications to Storage and Microelectromechanical Systems (MEMS),
Romankiw et al., Editors, PV 98-20, p. 646, The Electrochemical
Society Proceedings Series, Pennington, N.J. (1999); M. Schwartz,
N. V. Myung, and K. Nobe, J. Electrochem. Soc., 151, C468,
(2004).]. The research focus of this dissertation is on the
co-deposition of Co--Sm alloys to fabricate high performance
SmCo.sub.5 and Sm.sub.2Co.sub.17 permanent magnets, which promise
much lower costs, more flexibility than existing manufacturing
processes.
C. Cobalt-Samarium Magnets
[0175] Co--Sm magnets are known for magnetocrystalline anisotropy,
high coercivity, and maximum energy products. These characteristics
are based mainly on the intermetallic phases, SmCo.sub.5 and
Sm.sub.2Co.sub.16. SmCo.sub.5 magnets have the highest uniaxial
anisotropies of any class of magnets, Ku (uniaxial magnetic
anisotropy energy coefficient).apprxeq.10.sup.7 J/m.sup.3. On the
other hand, Sm.sub.2Co.sub.17 magnets exhibit high flux density and
Curie temperature. Metastable phases, intermetallic compounds, and
crystalline structures of Co--Sm alloys are the important
properties that provide superior permanent magnet performance. The
unique properties of SmCo.sub.5 and Sm.sub.2Co.sub.17 magnets will
be reviewed.
[0176] Different kinds of manufacturing methods for fabricating
Co--Sm magnets have been developed the past 40 years. Bonding and
sintering [M. G. Benz and D. L. Martin, Appl. Phys. Letters, 17,
176, (1970); M. G. Benz and D. L. Martin, J. Appl. Phys., 43, 4733,
(1972); A. E. Ray and K. J. Strnat, IEEE Trans. Magnetics, Mag-11,
1429, (1975); Z. A. Abdelnour, H. F. Mildrum and K. J. Strnat, IEEE
Trans. Magnetics, Mag-16, 1980, (1980)] and mechanical alloying [J.
Wecker, M. Katter and L. Schultz, J. Appl. Phys., 69, 6085, (1991);
S. K. Chen, J. L. Tsai and T. S. Chin, J. Appl. Phys., 81, 5631,
(1997); M. L. Kahn, J. L. Bobet, F. Weil and B. Chevalier, J.
Alloys Comp., 334, 285, (2002); J. Zhou, R. Skomski and D. J.
Sellmyer, J. Appl. Phys., 93, 6495, (2003)] are the main methods
for processing large Co--Sm magnets for common applications (e.g.,
automotive, domestic, electronic, aerospace devices). Applications
for information storage, microelectromechanical systems (MEMS), and
nanoelectromechanical systems (NEMS) have lead to developments of
thin film processes such as DC sputtering, RF sputtering, PVD, and
pulsed laser deposition. The preparation of thin film Co--Sm
magnets not only lead to new industrial applications but also
improve performance. Thin film processes for Co--Sm magnets are
disclosed.
[0177] 1. Co--Sm Alloy System
[0178] The potential superior magnetic properties of intermetallic
compounds of Sm and Co was the focus of Buschow et al.'s [K. H. J.
Buschow and W. A. J. J. Velge, J. Less-Common Met., 13, 11, (1967);
K. H. Buschow and A. S. V. D. Goot, J. Less-Common Met., 14, 323,
(1967)] investigation of the entire concentration range of binary
Sm--Co alloys by X-ray diffraction, thermoanalytical and
metallographic methods. The phase diagram is shown in FIG. 2.
Intermetallic compounds of Sm.sub.3Co, Sm.sub.9Co.sub.4,
SmCo.sub.2, SmCo.sub.3, Sm.sub.2Co.sub.7, SmCo.sub.5 and
Sm.sub.2Co.sub.17 were obtained.
[0179] Three eutectics between the phases Sm--Sm.sub.3Co,
Sm.sub.9Co.sub.4--SmCo.sub.2 and Sm2Co.sub.17--Co were found. FIG.
3 shows the Co-rich region of the Co--Sm phase diagram [K. J.
Strnat, Ferromagnetic materials, Vol 4, E. P. Wohlfarth and K. H.
J. Buschow, Editors, Elsevier Science Publishers, New York, (1998),
p. 143] after den Broeder and Buschow (1972), Perry (1977), and Ray
(1986). From the phase diagram, both SmCo.sub.5 and
Sm.sub.2Co.sub.17 are identified as intermetallic compounds.
Sm.sub.2Co.sub.17 is a stable phase and its melting point is about
1335.degree. C. On the other hand, SmCo.sub.5 is a metastable phase
existing above 805.degree. C. (eutectoid point).
[0180] 2. Properties of SMCO.sub.5 and SM.sub.2CO.sub.17
Magnets
[0181] The hexagonal CaCu.sub.5 structure of SmCo.sub.5 [C. Barrett
and T. B. Massalski, Structure of metals, Pergamon Press, Oxford,
New York, (1980), p 266] is shown in FIG. 4. A smaller hexagonal Co
combined within a hexagonal Sm in the same plane (layer A and C). A
similar hexagonal Co plane rotated by 30.degree. (layer B) is
inserted between two hexagonal Sm planes (layer A and C).
[0182] Single-phase SmCo.sub.5 [R. C. O'Handley, Modern magnetic
materials, John Wiley & Son, Inc., New York, (2000), pp.
496-502] has exhibited room temperature coercivity (H.sub.c) of
0.72 MA/m (9 kOe), maximum energy product of over 200 kJ/m.sup.3
(24 MGOe) and saturation magnetization (Ms) of 1 T. A high Curie
point (T.sub.c=685.degree. C.) enables a wide range of
applications. The high coercivity of SmCo.sub.5 is attributed to
reversal domain nucleation controlled by grain boundaries [J. D.
Livingston, AIP Conf Proc., 10, 643 (1973)] restricting the
mobility of domain walls leading to high coercivity.
[0183] The rhombohedral Th.sub.2Ni.sub.17-type structure of
Sm.sub.2Co.sub.17 [R. C. O'Handley, Modern magnetic materials, John
Wiley & Son, Inc., New York, (2000), pp. 496-502] is shown in
FIG. 5. This structure has the same cobalt hexagonal nets as
SmCo.sub.5 but with fewer Sm atoms in adjacent layers. The
magnetocrystalline anisotropy of Sm.sub.2Co.sub.17 magnets
(Ku.apprxeq.3.times.10.sup.6 J/m.sup.3) is less than SmCo.sub.5
magnets (K.apprxeq.10.sup.7 J/m.sup.3) as well as its coercivity of
0.68 MA/m (8.5 kOe). Saturation magnetization of 1.2-1.5 T (109-137
emu/g) and Curie temperature (T.sub.c) of 810-970.degree. C. are
higher, however. The grains of Sm2Co.sub.17 magnets containing fine
structures of SmCo.sub.5 pin the domain walls [P. Campbell,
Permanent magnet materials and their application, Cambridge
University Press, New York, (1994), pp. 42-43] and can be achieved
by proper heat treatment. The pinning mechanism is shown as FIG.
6.
[0184] Chemical reduction is usually used to produce Co--Sm powders
[P. Campbell, Permanent magnet materials and their application,
Cambridge University Press, New York, (1994), pp. 38-45]. Co--Sm
magnets can be obtained by sintering Co--Sm powders, molding bonded
Co--Sm particles, mechanical alloying, and thin film processes,
such as sputter and PVD. After optimization of heat treatment, high
coercivities and anisotropic magnetic properties can be
achieved.
[0185] 3. Thin Film Technology of Co-Sm Magnets
[0186] a. DC Sputtering
[0187] The first Co--Sm thin film was prepared in 1969 by getter
sputtering [H. C. Theuerer, E. A. Nesbitt, and D. D. Bacon, J.
Appl. Phys., 40, 2994, (1969)] for comparison with the unusually
high coercivity (28.7 kOe, annealed at 400.degree. C.) of sintered
Co.sub.5-xCu.sub.xSm alloys found by E. A. Nesbitt et al. [E. A.
Nesbitt, R. H. Willens, R. C. Sherwood, E. Buehler, and J. H.
Wernick, Appl. Phys. Letters, 12, 361, (1968).]. The later obtained
Co--Sm thin films, with/without addition of Cu, with very high
coercivities were dependent strongly on substrate temperatures
(bell-shaped curves), and higher than bulk specimens.
[0188] Theuerer et al. reported a maximum coercivity of 20 kOe for
SmCo.sub.5 obtained with films (400 nm) prepared at 600.degree. C.
which is much higher than the value of only 1 kOe for bulk
specimens of the same composition [H. C. Theuerer, E. A. Nesbitt,
and D. D. Bacon, J. Appl. Phys., 40, 2994, (1969)]. For the
Co.sub.5-xCu.sub.xSm (x=1.35) alloys, films (400 nm) prepared at
500.degree. C. had a maximum coercivity of 30 kOe which is greater
than bulk specimens (12 kOe). Thick films (.about.5 um) prepared at
500-600.degree. C. for the respective alloy compositions had lower
coercivities (13.3 kOe) than thin films (30 KOe, 400 nm) and close
to the bulk values (12 KOe). Films deposited on crystalline
substrates resulted in larger grain size with lower
coercivities.
[0189] Bendson and Judy [S. A. Bendson and J. H. Judy, IEEE Trans.
Magnetics, 9, 627, (1973)] used DC triode sputtering to obtain
Co--Sm thin films (100 to 500 nm) at 10.sup.-3 Torr of Ar on glaze
alumina substrates at or above 600.degree. C. from Co and Sm
targets. Saturation magnitization, coercivity and squareness of
deposits are shown in FIG. 7. The saturation magnitization is
reduced by increasing Sm content until the mixture becomes
paramagnetic between 25 and 30 atomic percent Sm (FIG. 7) in
agreement with the published value for bulk specimens [R. Lemaire,
R. Pauthenet and J. Schweizer, IEEE Trans. Magnetics, Mag-6, 153,
(1970)]. In addition, low coercivity is observed over the major
range of composition except among 22 at % Sm where extremely high
coercivity is found. In these films, the easy axis lies in the film
plane. Addition of Sm apparently results in decreased
squareness.
[0190] Zhang et al. [C. Zhang, R. Liu and G. Feng, IEEE Trans.
Magnetics, 16, 1215, (1980)] studied non-crystalline SmCo.sub.5 and
Sm.sub.0.5MM'.sub.0.5Co (MM': Ce 50%, La 20%, Nd 10%, Pr 10%) thin
films (0.7 to 1.4 m) by DC diode sputtering on a liquid nitrogen
cooled glass substrate. Even after heat treatment at 750.degree. C.
for 4 hours, crystalline SmCo.sub.5 was not formed. The coercivity
is only about several hundred Oe which is far below 20 KOe obtained
by Theuerer et al. [H. C. Theuerer, E. A. Nesbitt, and D. D. Bacon,
J. Appl. Phys., 40, 2994, (1969)]. On the other hand, due to the
formation of crystalline (.beta.-Co (fcc), saturation magnetization
of SmCo.sub.5 non-crystalline films were about 620-663G (74-79
emu/g) and increased to 810-880 G (97-105 emu/g) after heat
treatment at 600.degree. C. for 2 hours.
[0191] Co--Sm thin films (79 at % Co, 21 at % Sm, 24 nm) on Cr (95
nm) were first studied in 1994 by DC magnetron sputtering (no heat
treatment) [Y. Liu, B. W. Robertson, Z. S. Shan, S. Malhotra, M. J.
Yu, S. K. Renukunta, S. H. Liou and D. J. Sellmyer, IEEE Trans.
Magnetics, 30, 4035, (1994)]. It was found that the volume fraction
of the crystallites decreased from 91 to 54 at % as the Ar pressure
increased from 0.5.times.10.sup.-4 to 3.times.10.sup.-4 Torr the
maximum coercivity of 2.58 kOe was obtained at 1.2.times.10.sup.-4
Torr.
[0192] Mizukami et al. [M. Mizukami, T. Abe and T. Nishihara, IEEE
Trans., Magnetics, 33, 2977, (1997)] found that the coercivity of
DC sputtered Co--Sm thin film decreased by 50% after exposure to
air for 30 hours because Sm was oxidized. A protective Cr layer
coating reduced oxidation by forming a Cr/CoSm/Cr structure. Takei
et al. [S. Takei, A. Morisako and M. Matsumoto, J. Appl. Phys., 81,
4674, (1997)] found that the coercivity of Co--Sm (20 at % Sm) thin
films increased linearly with the increasing Ar pressure. The
squareness ratio of 0.92 could be obtained with a highly
crystallized Cr underlayer (P.sub.Ar of 10.sup.-3 Torr). These
values suggest that an easy axis of magnetization for the CoSm thin
film is in-plane. The coercivity and squareness (1.95 kOe and 0.92,
respectively) of CoSm thin film (20 at % Sm) with Cr underlayer in
this study is higher than that obtained by Bendson and Judy (0.7
kOe and 0.6) [S. A. Bendson and J. H. Judy, IEEE Trans. Magnetics,
9, 627, (1973)].
[0193] The effects of oxidation on the magnetic and electrical
properties of DC sputtered CoSm thin films were studied by Cho et
al. [H. S. Cho, J.R. Salem, A.J. Kellock and R. B. Beyers, IEEE
Trans. Magnetics, 33, 2890, (1997)]. Co--Sm films prepared on Si
(100) and quartz glass by DC magnetron sputtering of different
composition and substrate temperatures were characterized. The
results are summarized in FIG. 8. Co--Sm films deposited at room
temperature were non-crystalline, and the coercivity increased from
20 to 300 Oe and the magnetization saturation decreased from 1400
to 500 emu/cm.sup.3 (154 to 60 emu/g or 1.76 to 0.63 T) with
increasing Sm deposit content from 0 to 28 at %. With increased
substrate temperature from 25 to 350.degree. C., the coercivity
increased from 200 to 8000 e and the magnetization saturation
decreased from 500 to 380 emu/cm.sup.3 (60 to 46 emu/g or 0.63 to
0.48 T).
[0194] Cho et al. believed that these different behaviors depend on
the extent of oxidation in the film especially at high substrate
temperatures [H. S. Cho, J. R. Salem, A. J. Kellock and R. B.
Beyers, IEEE Trans. Magnetics, 33, 2890, (1997)]. More than 10 at %
oxygen was present in sputtered deposits at room temperature, and
the amount of oxygen increased with substrate temperature. TEM
results indicated that Co--Sm thin films deposited at 360.degree.
C. were multiphase mixtures of Sm.sub.2O.sub.3 and Co-enriched
phases rather than a simple homogeneous Co--Sm phase.
[0195] In 1998 Liu et al. [Y. Liu, R. A. Thomas, S. S. Malhotra, Z.
S. Shan, S. H. Liou and D. J. Sellmyer, J. Appl. Phys., 83, 6244,
(1998)] studied phase formation and magnetic properties of Co--Sm
thin films (DC magnetron sputtering) by increasing thickness with a
Cr cover layer as Mizukami et al [M. Mizukami, T. Abe and T.
Nishihara, IEEE Trans., Magnetics, 33, 2977, (1997)] compared to
his previous work [Y. Liu, B. W. Robertson, Z. S. Shan, S.
Malhotra, M. J. Yu, S. K. Renukunta, S. H. Liou and D. J. Sellmyer,
IEEE Trans. Magnetics, 30, 4035, (1994)]. It was found that for
deposits (19 at % Sin, 360 nm) obtained at Ar pressure of
2.times.10.sup.-4 Torr then annealed at 600.degree. C. has
SmCo.sub.5 phases and an extremely high coercivity of 45 kOe. TEM
showed a new phase SmCo.sub.3 (22 at % Sm) was formed when the film
was annealed at 500.degree. C.
[0196] Prados et al [C. Prados and G. C. Hadjipanayis, J. Appl.
Phys., 83, 6253, (1998); C. Prados and G. C. Hadjipanayis, Appl.
Phys. Letters, 74, 430, (1999); C. Prados, A. Hernando, G. C.
Hadjipanayis and J. M. Gonzaleza, J. Appl. Phys., 85, 6148, (1999)]
sputtered Sm(Co, Ni, Cu) thin films (500 nm) on Cr underlayers (300
nm) on water cooled Si to promote a c-axis texture along the
in-plane direction in order to increase their in-plane magnetic
anisotropy. After films obtained from DC magnetron sputtering, the
thin films were annealed in a vacuum greater than 10.sup.-5 Torr at
400 to 650.degree. C. for 30 min. Crystallization of the
non-crystalline magnetic films (obtained at room temperature)
produced a huge enhancement of coercivity (from 100 to more than 40
kOe). High angle XRD patterns indicate that the Cr underlayers grew
with a (110) texture, and the Sm(Co, Ni, Cu) thin films were
non-crystalline as deposited. After annealing, the (111) plane of
SmCo.sub.5 appeared and optimum samples indicated a nanocrystalline
structure (particle size of 10 nm).
[0197] After Liu and Prados showed that the Cr underlayer plays a
significant role in the magnetic properties of Co--Sm thin films,
Takei et al. [S. Takei, A. Morisako and M. Matsumoto, J. Appl.
Phys., 87, 6968, (2000)] worked on the effect of different kinds of
underlayers, such as Cr, Mo, W, W/Cr and Al. The coercivity of the
films with Cr and Mo underlayer were larger than 3 kOe for
underlayers thicker than 100 nm. The squareness of the films with
Cr and Mo underlayers were higher than 0.85 and 0.94, respectively.
The result indicated that both Cr and Mo are suitable for SmCo
films with in-plane magnetic anisotropy. For ultra-thin Co--Sm
films (2.5 nm) deposited on Cr underlayer (100 nm) on Corning #7059
glass the XRD pattern indicated that the Sm--Co layer crystallized
by substrate heating with coercivity higher than 3 kOe. Substrate
heating during deposition was effective in preparing ultrathin
Sm--Co thin films with higher coercivity.
[0198] There have been many in-plane magnetic anisotropy studies of
Co--Sm thin films but few of perpendicular magnetic anisotropy.
Recently, Sayama et al. [J. Sayama, T. Asahi, K. Mizutani and T.
Osaka, J. Phys. D: Appl. Phys., 37, L1, (2004); J. Sayama, K.
Mizutani, T. Asahi, J. Ariake, K. Ouchi, S. Matsunuma and T. Osaka,
J. Magn. Magn. Mater., 287, 239, (2005)] DC sputtered CoSm thin
films [Co(0.41 nm)/Sm(0.31 nm)].sub.35 on Cu underlayer (100 nm) on
a glass substrate at various temperatures. Coercivity increased
rapidly between 325-345.degree. C. and was greater in the
perpendicular direction than the in-plane direction. The Co/Sm
laminate structure on Cu underlayer was the key in the
crystallization of SmCo.sub.5 with its c-axis perpendicular to the
film plane. The perpendicular magnetic anisotropy was further
improved by reducing the surface roughness of the Cu
underlayer.
[0199] Takei et al. [S. Takei, A. Morisako and M. Matsumoto, J.
Magn. Magn. Mater., 272-276, 1703, (2004)] obtained similar results
to Sayama et al. [J. Sayama, T. Asahi, K. Mizutani and T. Osaka, J.
Phys. D: Appl. Phys., 37, L1, (2004); J. Sayama, K. Mizutani, T.
Asahi, J. Ariake, K. Ouchi, S. Matsunuma and T. Osaka, J. Magn.
Magn. Mater., 287, 239, (2005)] and found that the Co--Sm layer
with (001) orientation was crystallized on top of the (111) Cu
orientation underlayer and perpendicular coercivity of the film was
about 9.6 kOe with substrate temperatures about 300.degree. C.
[0200] b. RF-Sputtering
[0201] Cadieu et al. [F. J. Cadieu, S. H. Aly and T. D. Cheung, J.
Appl. Phys., 53, 2401, (1982)] deposited Co--Sm thin films (1.61
lam) deposited on an Al.sub.2O.sub.3 substrate by RF-sputtering.
The composition of the Co--Sm thin films were close to the
composition SmCo.sub.5 and Sm.sub.2Co.sub.17. Hysteresis loops for
various Sm deposit content are shown in FIG. 9.
[0202] The low saturation magnitization measured perpendicular to
the film plane and the XRD patterns indicated that the c-axis is
strongly oriented in the film plane direction. This result is
similar to the crystalline Co--Sm thin films made by DC sputtering
onto heated substrate or by crystallization (annealing) of a
noncrystalline deposit. The energy product measured in the in-plane
direction was lower than bulk specimens which might be due to the
random orientation of the c-axis in the film plane.
[0203] Velu et al. [E. M. T. Velu and D. N. Lambeth, J Magn. Magn.
Mater., 69, 5175, (1991)] studied the Co--Sm thin films
with/without Cr underlayer on 7059 Coming glass and NiP coated Al
substrates. The coercivity of the CoSm thin films was higher for Cr
underlayers deposited at 10.sup.-2 Torr Ar pressure. The coercivity
decreased with higher substrate temperature (>300.degree. C.)
which might due to the crystallographic texture transformation of
Cr from <110> to <200> orientation. A maximum
coercivity of 2.4 kOe and squareness of 1 were obtained for CoSm
thin films (14nm) under optimal conditions.
[0204] Chen et al. studied the induced anisotropy [K. Chen, H.
Hegde and F. J. Cadieu, Appl. Phys. Letters, 61, 1861, (1992)] and
different other types of anisotropy [K. Chen, H. Hegde, S. U. Jen
and F. J. Cadieu, J Appl. Phys., 73, 5923, (1993)] in RF sputtered
non-crystalline Sm--Co thin films on water cooled polycrystalline
Al.sub.2O.sub.3 substrates. An in-plane magnetic field was applied
during RF sputtering. Both in-plane and perpendicular anisotropy
were found depending on the sputtering conditions. Three different
sources of anisotropy can be distinguished in these films. The
in-plane anisotropy was explained as directional pair ordering;
perpendicular anisotropy was only observed for films deposited
through sputtering at room temperature; a much larger anisotropy
was observed at higher deposition temperatures with the easy axis
in the film plane.
[0205] Neu et al. [V. Neua and S. A. Shaheen, J. Appl. Phys., 86,
7006, (1999)] RF-sputtered SmCo.sub.5 and Sm(CoFeCuZr).sub.7 thin
films (1 .mu.m) on heated polycrystalline Al.sub.2O.sub.3
substrates. With increased Sm deposit content, Sm--Co thin films
transformed from the TbCu.sub.7-type to the CaCu.sub.5-type
structure at around 17 at % Sm in agreement with the stoichiometric
SmCo.sub.5 (16.7 at %). With increasing Sm content, the c-axis of
SmCo.sub.5 preferred to lie on the film plane. The morphology
showed larger and more elongated grains with increasing Sm content
which might be due to a higher surface mobility of Sm-rich samples.
Higher Sm content resulted in higher coercivity and lower
Mrperpendicular/Mr parallel values (FIG. 10), the result of
crystallization of SmCo.sub.5.
[0206] c. PVD
[0207] Geiss et al. [V. Geiss, E. Kneller and A. Nest, Appl. Phys.,
A27, 79, (1982)] studied non-crystalline Sm.sub.100-xCo.sub.x
(70<x<90) thin films (150 nm) prepared by vapor deposition on
flat glass substrates at room temperature. A magnetic field of 500
Oe was applied parallel to the film plane during evaporation. After
deposition, specimens were aged at various temperatures. The easy
axis of magnetization lay on film plane and deposits appeared
non-crystalline magnets. The coercivity varied between 30 to 3000
Oe, depending on the composition, temperature and heat treatment.
Aging of any sample at temperatures below the crystallization
temperature resulted in a decrease in coercivity.
[0208] Gronau et al. [M. Gronau, H. Goeke, D. SchUffler and S.
Sprenger, IEEE Trans. Magnetics, Mag-19, 1653, (1983)] prepared
non-crystalline Sm.sub.1-xCo.sub.x (0.67<x<0.91) thin films
(10 to 350 nm) by flash-evaporation of SmCo-alloy powder on glass
substrates. Saturation magnitization decreased linearly with
increasing Sm content with the same slope as the crystalline
material, but differences were about 10% smaller for the
non-crystalline phase in agreement with the results of DC sputtered
deposits by Bendson and Judy [S. A. Bendson and J. H. Judy, IEEE
Trans. Magnetics, 9, 627, (1973)]. For x=0.67 (SmCo.sub.2) crystals
were nonmagnetic with Ms nearly zero. The coercivity increased,
reached a maximum of 53 kA/m (650 Oe) at x=0.74, then decreased.
They concluded that there was little difference for films prepared
by evaporation on heated substrate or annealed at the same
temperature.
[0209] Following Geiss [K. Chen, H. Hegde, S. U. Jen and F. J.
Cadieu, J Appl. Phys., 73, 5923, (1993)] and Gronau [M. Gronau, H.
Goeke, D. SchUffler and S. Sprenger, IEEE Trans. Magnetics, Mag-19,
1653, (1983)], Kullmann et al. [U. Kullmann, E. Koester and C.
Dorsch, IEEE Trans. Magnetics, Mag-20, 420, (1984)] prepared
non-crystalline Sm.sub.100-xCo.sub.x (75<x<90) thin films
(100 nm) by PVD to obtain high density longitudinal recording. With
increasing Sm content, the coercivity increased from 30 to 100 kA/m
(375 to 1250 Oe). The saturation magnetization was decreased with
decreased Sm content.
[0210] The recording performance showed an improvement in recording
density and signal-to-noise ratio compared to traditional
longitudinal recording media.
[0211] 4. Electrodeposition of Co-RE (Rare Earth) Alloys
[0212] a. Electrodeposition of Co-RE Alloys from Non-Aqueous
Solutions
[0213] In 1953, Moeller et al. [T. Moeller and P. A. Zimmerman, J.
Am. Chem. Soc, 75, 3940, (1953); T. Moeller and P. A. Zimmerman,
Science, 120, 539, (1954)] dissolved anhydrous yttrium acetate,
neodymium bromide and lanthanum nitrate in anhydrous
ethylenediamine and monoethanolamine to obtain yttrium, neodymium
and lanthanum. Electrolyses of ethylenediamine solutions gave
metallic cathode deposits with all salts tested, but deposits were
not obtained from monoethanolamine solutions due to low solubility
and conductivities. All deposits exhibited rare-earth metal
properties, such as oxidation in air or in water and hydrogen
evolution from hydrochloric acid solution.
[0214] Increased interest in higher performance Co--Sm magnets
(SmCo.sub.5 and Sm.sub.2Co.sub.17) lead to studies of the
electrodeposition of Co-Sin alloys from non-aqueous media since
aqueous electrodeposition of Co--Sm alloys was extremely difficult,
if not impossible, due to excessive hydrogen evolution. [Y. Sato,
H. Ishida, K. Kobayakawa and Y. Abe, Chemistry Letter, 1471 (1990);
T. Lida, T. Nohira and Y. Ito, Electrochim. Acta, 48, 901, (2003);
T. Lida, T. Nohira and Y. Ito, Electrochim. Acta, 48, 2517, (2003);
P. Liu, Y. Du, Q. Yang, Y. Tong and G. A. Hope, J. Magn. Magn.
Mater., 153, C57, (2006)]
[0215] Sato et al. [Y. Sato, T. Takazawa, M. Takahashi, H. Ishida
and K. Kobayakawa, Plat. Surf Finish, 72, 80, (1993); Y. Sato, H.
Ishida, K. Kobayakawa and Y. Abe, Chemistry Letter, 1471 (1990)]
electrodeposited non-crystalline Sm--Co thin films from a formamide
solution containing anhydrous samarium and cobalt chloride. The
deposits were confirmed as metallic by XPS. The results suggested
that the deposit contains Co-rich compounds such as
Sm.sub.2Co.sub.17 and SmCo.sub.3, which show ferromagnetism.
However, after deposits were heat treated at 600.degree. C. for 3
hours, cobalt oxides were found in the specimens. The magnetic
properties of deposits after annealing did not improve. The highest
coercivity before heat treatment was about 90 Oe and after heat
treatment at 600.degree. C. for 3 hours about 562 Oe.
[0216] In 2003, Iida et al. studied the electrodeposition of Sm--Co
alloys at a Co cathode in a molten LiCl--KCl--SmCl.sub.3 system [T.
Lida, T. Nohira and Y. Ito, Electrochim. Acta, 48, 901, (2003)] at
723 K. In addition, a molten LiCl--KCl--SmCl.sub.3--CoCl.sub.2
system [T. Lida, T. Nohira and Y. Ito, Electrochim. Acta, 48, 2517,
(2003)] at 450.degree. C. using a Cu substrate also had been
studied. Phases of the deposited Sm--Co alloys could be controlled
by the potential. Sm.sub.2Co.sub.17, SmCo.sub.3, SmCo.sub.2, and
Li.sub.xSm.sub.4Co.sub.6 were found at the potentials of 1.4, 0.8,
0.3 and 0.05V (vs. Li.sup.+/Li). However, the deposit rate was slow
(0.004-5 um/hr) and magnetic properties were not measured.
[0217] Recently, in 2006, Liu et al. [P. Liu, Y. Du, Q. Yang, Y.
Tong and G. A. Hope, J. Magn. Magn. Mater., 153, C57, (2006)]
codeposited Sm--Co non-crystalline films in a
urea-acetamide-NaBr-MCl melt (M=Sm or Co). They found that the
reduction of Co is irreversible and Sm cannot be reduced alone in
these melts and applied the idea of a polynuclear complex mechanism
as proposed by Schwartz et al [N. V. Myung, M. Schwartz, and K.
Nobe, in Fundamental Aspects of Electrochemical Deposition and
Dissolution, M. Matlosz, D. Landolt, R. Aogaki, Y. Sato, and J. B.
Talbot, Editors, PV 99-33, p. 263, The Electrochemical Society
Proceedings Series, Pennington, N.J. (1999).] in the glycine
aqueous system. The Sm--Co films were non-crystalline as deposited,
and intermetallic Sm--Co phases were found after heat treatment at
900.degree. C. Unfortunately, the saturation magnetization of a
deposit of 3.3 at % Sm is only 2.9 emu/g (before heat treatment)
which is too low compared to DC sputtering (143 emu/g) for a
similar alloy composition. The highest coercivity of deposits after
heat treatment (900.degree. C., 3 hr) was 180 Oe (60 at % Sm) with
saturation magnetization of 1.66 emu/g.
b. Electrodeposition of IG-W, Mo and V Alloys
[0218] Brenner suggested that although metals with extreme negative
reduction potentials, such as W, Mo and V, cannot be deposited from
aqueous media individually, co-deposition with the iron group
metals can be achieved. Review of representative investigations of
these alloys follow:
[0219] c. IG-W Alloys
[0220] Holt and his student [J. Seim and M. L. Holt, Trans.
Electrochem. Soc., 95, 205 (1949); D. W. Ernst, R. F. Amlie and M.
L. Holt, J. Electrochem. Soc., 102 (8), 461 (1955); D. W. Ernst and
M. L. Holt, Ibid., 105 (11), 686 (1958).] co-electrodeposited IG-W
alloys from ammoniacal solutions containing organic hydroxyl acids,
such as citric, tartric, and malic acid. Hydroxyl acids, which are
known as good complexing agents, increased current efficiency and
tungstate solubility to obtain smooth IG-W deposits. The reduction
of the tungstate was suggested due to the catalysis of atomic
hydrogen reduction by a two-step reduction hypothesis.
[0221] Brenner et al. [A. Brenner, P. Burkheard and E. Seegmiller,
J. Res. NBS, 94, 351 (1947).] developed a codeposition process of W
and iron group alloys from aqueous ammoniacal solutions
(.about.pH8.5) containing appropriate metal salts (sodium tungstate
and 1G (iron group)-chloride or IG-sulfate) and certain
hydroxyl-organic acids (citric acid, tartaric acid, hydroxyacetic
acid, malic acid, gluconic acid). They concluded that the W ion
concentration is the most important variable affecting W deposit
content, which increased and reached a limit with increasing W
concentrations. The maximum W deposit content of Co--W and Fe--W
alloys was about 23 to 32 at %, and about 12 at % for Ni--W alloys.
W deposit content increased with CD, but did not significantly
change with temperature. However, current efficiency increased
considerably with increase in temperature.
[0222] Schwartz (1948) developed a commercial Co--W plating process
using an ammoniacal citrate bath [M. Schwartz, unpublished data,
1948-55; see also discussion in Trans. Electrochem. Soc., 94, 382
(1948)]. He found that when the Co and. WO.sub.4.sup.2- salt
solutions are mixed, a cobalt tungstate precipitate forms which
dissolves with addition of citrate. His experimental results lead
him to conjecture that both Co(I1) and W(VI) are coordinated in the
same complex with deprotonation of the carboxylate forming a
heteronuclearbiscitrato complex [M. Schwartz and K. Nobe, Trans.
Electrochem. Soc., 1, 103 (2006)].
[0223] Recently, Gileadi and his coworkers [Younes and E. Gileadi,
J. Electrochem. Soc., 149, C100, (2002); Younes-Metzler, L. Zhu and
E.Gileadi, Electrochim. Acta, 48, 2551, (2003)] obtained high W
deposit (.about.67 at %) content Ni--W alloys from non-ammonia
plating baths. However, current efficiency was reduced
dramatically. The formation of a heteronuclear Ni--W monocitrato
complex, [Ni(WO.sub.4)(cit)(H)].sup.2- was proposed as to
co-deposition of the Ni--W alloy.
[0224] d. IG-Mo Alloys
[0225] Holt and co-workers [L. E. Vaaler and M. L. Holt, Trans.
Electrochem. Soc. 90, 43 (1946); L. E. Vaaler and M. L. Holt,
Ibid., 94, 50 (1948); W. E. Clark and M. L. Holt, Ibid., 94, 244
(1948); M. H. Lietzke and M. L. Holt, Ibid., 94, 252 (1948); R. F.
McElwee and M. L. Holt, J. Electrochem. Soc., 99 (2), 48 (1952).]
extended their co-deposition studies of IG-W alloys to IG-Mo alloys
from equivalent solutions. Hull Cells were initially used to
determine operating conditions, such as pH, temperature, CD ranges
for bright, metallic deposits. Similar to IG-W co-deposition,
deposit Mo contents depended on the co-depositing IG metal with
Fe>Co>Ni. Current efficiencies decreased with increased Mo
content: Ni>Co>Fe. Complexation with citrate and tartrate
were favored for Ni--Mo codeposition with malate (and malic acid)
and glycolic acids for Co--Mo. Sodium citrate was superior to
citric acid or ammonium citrate.
[0226] Landolt and Podlaha have published a series of papers [E. J.
Podlaha and D. Landolt, J. Electrochem. Soc., 143, 885, (1996); E.
J. Podlaha and D. Landolt, J. Electrochem. Soc., 143, 893, (1996);
E. J. Podlaha and D. Landolt, Electrochem. Soc., 144, 1672, (1997)]
on the codeposition of Ni-Mo alloys using rotating cylinder
electrodes from the plating solutions of NH.sub.3,
C.sub.6H.sub.5Na.sub.3O.sub.7.2H.sub.2O,
Na.sub.2MoO.sub.4.2H.sub.2O, and NiSO.sub.4.6H.sub.2O. Alloy
composition was affected by CD, electrode rotation rate, solution
temperature, and species concentration, and Ni--Mo alloys of Mo
content in excess of 50 wt % have been deposited [E. J. Podlaha and
D. Landolt, J. Electrochem. Soc., 143, 885, (1996)]. For
electrolytes of low Mo concentration in the present of excess Ni
concentration, Mo content increased with increased electrode
rotation rate and decreased with increased CDs. On the other hand,
for electrolytes of low Ni concentration in the present of excess
Mo concentration, Mo contents were independent of convection. A
steady-state mathematical model was developed to predict the
codeposition of Ni--Mo alloys [E. J. Podlaha and D. Landolt, J.
Electrochem. Soc., 143, 893, (1996)]. This model assume that both
Ni and Mo can complex with citrate in alkaline solutions, but the
formation constant of Mo-citrate constant is much smaller than that
of the Ni-citrate complex. The model predictions were in agreement
with the observed trends in the experimental data [E. J. Podlaha
and D. Landolt, J. Electrochem. Soc., 143, 885, (1996)]. Rotating
cylinder electrodes of NiMo, CoMo, and FeMo alloys were
electrodeposited for Mo solution concentrations much lower than the
iron group species [E. J. Podlaha and D. Landolt, Electrochem.
Soc., 144, 1672, (1997)]. Mo deposit content was higher in CoMo
than NiMo and FeMo deposits due to a lower deposition rate of Co
than Ni and Fe.
[0227] e. IG-V Alloys
[0228] Arcos et al. [C. Arcos, M. Schwartz and K. Nobe, AVG',
Electrochem. Soc., 95-15, 193, (1994); M. Schwartz, C. Arcos and K.
Nobe, Plat. Surf Fin., 90, (6), 46, (2003)] reported the
co-deposition (citrate baths) of binary and ternary alloys of the
iron group metals and vanadium (i.e. Fe--V, Ni--V, Co--V,
Co--Ni--V, Ni--Fe--V and Co--Fe--V) by DC and PC. Generally,
vanadium deposit content increased with increase in pH (from 5.5 to
7.5) and increased CD (from 5 to 10 A/cm.sup.2). In binary alloys,
at pH 7, V content decreased as: Fe>Ni>Co. Only Fe--V was
obtained at pH below 7. For ternary alloys, the Co and V content
increased and Fe decreased by increased pH for Co--Fe--V alloys.
Convective mass transport and longer off time (PC) resulted in
increased V deposit content. Co-deposited Co--Fe--V alloys had
higher saturation magnetization compared to Ni--Fe (Perrnalloy type
alloys) deposits for both DC and PC. The corrosion resistance of
the deposits decreased as: Ni--Fe (DC)>Co--Fe--V
(PC)>Co--Fe--V (DC)>Co--Fe (DC).
[0229] You et al. [B. Y. Yoo, M. Schwartz, and K. Nobe,
Electrochim. Acta, 50, 4335, (2005)] investigated the
electrodeposition of IG-V binary alloys from citrate solutions.
Addition of NH.sub.3 and increasing pH lead to increase in V
deposit content, but non-metallic deposits were obtained at
solution pH>7. Increasing CD resulted in a linear decrease of V
deposit content and a sharp decrease of current efficiency. In
general, the V deposit content increased as follows: Ni (1 wt
%)<Fe (2 wt %)<<Co (4 wt %).
[0230] 5. Electrodeposition of Co-RE Alloys from Aqueous
Solutions
[0231] Compared to non-aqueous investigations, few studies of the
codeposition of Co--Sm alloys from aqueous solution have been
reported. Most of these studied were done by the UCLA group [L.
Chen, M. Schwartz, and K. Nobe, in Electrodeposited Thin Films, M.
Paunovic and D. A. Scherson, Editors, PV 96-19, p. 239, The
Electrochemical Society Proceedings Series, Pennington, N.J.
(1996); M. Schwartz, F. He, N. Myung, and K. Nobe, in Magnetic
Materials, Processes,and Devices V. Applications to Storage and
Microelectromechanical Systems (MEMS), L. T. Romankiw, S. Krongelb,
and C. H. Ahn, Editors, PV 98-20, p. 646, The Electrochemical
Society Proceedings Series, Pennington, N.J. (1999); N. V. Myung,
M. Schwartz, and K. Nobe, in Fundamental Aspects of Electrochemical
Deposition and Dissolution, M. Matlosz, D. Landolt, R. Aogaki, Y.
Sato, and J. B. Talbot, Editors, PV 99-33, p. 263, The
Electrochemical Society Proceedings Series, Pennington, N.J.
(1999); M. Schwartz, N. V. Myung, and K. Nobe, J. Electrochem.
Soc., 151, C468, (2004).]. Zangari synthesized Sm--Co nanoparticles
[J. Zhang, P. Evans, and G. Zangari, J. Magn. Magn. Mater., 283,
89, (2004).] by single short pulse electrodeposition from the
solution proposed by Schwartz et al. [M. Schwartz, N. V. Myung, and
K. Nobe, J. Electrochem. Soc., 151, C468, (2004).].
[0232] In 1996, Chen et al. [L. Chen, M. Schwartz, and K. Nobe, in
Electrodeposited Thin Films, M. Paunovic and D. A. Scherson,
Editors, PV 96-19, p. 239, The Electrochemical Society Proceedings
Series, Pennington, N.J. (1996).] published the first study of
IG-RE alloys from aqueous solution. Electrodepositions was carried
out at room temperature and pH 4 from the plating solution
containing RE mixtures, Co, Fe or Ni chloride salts, and various
addition agents; soluble anodes were used. In direct current (DC)
electrodeposition, it was noted that RE was not found in the
deposits from the solutions of pH<4. RE deposit content (Co-RE
and Ni-RE) increased with increasing current density (CD) from 5 to
20 mA/cm.sup.2. RE deposit content was higher for Fe-RE than Ni-RE
and Co-RE. In pulsed current (PC) electrodeposition, higher
temperatures and cobalt concentrations resulted in lower RE deposit
content. For codeposition of metallic IG-RE alloys, specific
addition agents (i.e. aminocarboxylates) in the plating solution
were required.
[0233] In 1998, Schwartz et al. [M. Schwartz, F. He, N. Myung, and
K. Nobe, in Magnetic Materials, Processes,and Devices V.
Applications to Storage and Microelectromechanical Systems (MEMS),
L. T. Romankiw, S. Krongelb, and C. H. Ahn, Editors, PV 98-20, p.
646, The Electrochemical Society Proceedings Series, Pennington,
N.J. (1999).] used plating solutions containing 0.3M RE metal ions
(i.e. La, Ce, Nd, Gd and RE mixtures), 0.12M IG ions, 0.36M
complexant (e.g., glycine, alanine and serine), 1M NH.sub.4Cl and
0.5M H.sub.3BO.sub.3 to obtain IG-RE alloys at room temperature. In
DC electrodeposition, it was found that the addition of NH.sub.4Cl
improved solution stability and deposit appearance. RE deposit
content decreased in the order: glycine>serine>alanine. With
glycine, the RE deposit content increased: Co<Fe<Ni. PC
electrodeposition extended the effective peak CD range for metallic
deposits. Crack density seemed to be directly related to the
deposit RE content.
[0234] In 1999, Myung et al. [N. V. Myung, M. Schwartz, and K.
Nobe, in Fundamental Aspects of Electrochemical Deposition and
Dissolution, M. Matlosz, D. Landolt, R. Aogaki, Y. Sato, and J. B.
Talbot, Editors, PV 99-33, p. 263, The Electrochemical Society
Proceedings Series, Pennington, N.J. (1999).] used chloride-based
plating solutions containing 0.3M RE ions (i.e. Nd or Sm), 0.12M IG
ions (i.e. Co and Ni), 0.36-0.72M glycine and 1M NH.sub.4Cl to
obtain 10-RE alloys at room temperature. 0-0.4M DMAB
(dimethylamineborane) was added to solutions to obtain ternary
RE-IG-B alloys. Soluble IG served as anodes, and brass and
stainless steel panels served as cathode substrates. Metallic
Nd--Ni--B alloys were electrodeposited at pH6 and CD<40
mA/cm.sup.2. Increased CD led to increased Nd content, decreased B
content and current efficiency. Increasing glycine/Ni ion
concentration decreased Nd content and increased current
efficiency. Metallic Sm--Co and Sm--Co--B alloys were obtained at
pH 4-6.5, CD<40 mA/cm.sup.2. In the absence of DMAB in
solutions, Sm content increased with increased CD; in the presence
of DMAB, the opposite trend was observed. The crystal structures of
Sm--Co and Sm--Co--B alloys were hexagonal closed pack (hcp)
(CD<10 mA/cm.sup.2) or non-crystalline (CD>10 mA/cm.sup.2)
Deposit grain size reduced from 128 to 38 nm by increased CD from 5
to 30 mA/cm.sup.2.
[0235] In 2004, Schwartz et al. [M. Schwartz, N. V. Myung, and K.
Nobe, J. Electrochem. Soc., 151, C468, (2004).] used chloride- or
sulfamate-based plating solutions containing 0.3 or 0.9M RE metal
ions (i.e. Ce, Nd, Gd and Sm), 0.12M IG ions (i.e. Fe, Co and Ni),
0.36M complexant (e.g., glycine, alanine and serine), 1M NH.sub.4
ions (i.e. NH.sub.4Cl or NH.sub.4NH.sub.7SO.sub.3) to obtain IG-RE
alloys at room temperature with soluble IG or insoluble Ti serving
as anodes. The result agreed with previous studies [L. Chen, M.
Schwartz, and K. Nobe, in Electrodeposited Thin Films, M. Paunovic
and D. A. Scherson, Editors, PV 96-19, p. 239, The Electrochemical
Society Proceedings Series, Pennington, N.J. (1996); M. Schwartz,
F. He, N. Myung, and K. Nobe, in Magnetic Materials, Processes, and
Devices V. Applications to Storage and Microelectromechanical
Systems (MEMS), L. T. Romankiw, S. Krongelb, and C. H. Ahn,
Editors, PV 98-20, p. 646, The Electrochemical Society Proceedings
Series, Pennington, N.J. (1999); N. V. Myung, M. Schwartz, and K.
Nobe, in Fundamental Aspects of Electrochemical Deposition and
Dissolution, M. Matlosz, D. Landolt, R. Aogaki, Y. Sato, and J. B.
Talbot, Editors, PV 99-33, p. 263, The Electrochemical Society
Proceedings Series, Pennington, N.J. (1999).] that the RE deposit
content increased with the increasing CD and solution pH. The Sm
deposit content ranked as: Fe>Ni=Co. Metallic Co--Sm deposits
did not extend beyond CD=400 mA/cm.sup.2 resulted in maximum Sm
deposit content of 8 at %. Aminoacids were found to be effective
complexing agents for the codeposition of RE alloys; glycine
resulted in higher RE deposit contents than serine and alanine
(glycine>serine>alanine) at room temperature. A mechanism for
the codeposition of IG-RE alloys was proposed involving
hetero-nuclear glycinato coordination complexes as a result of the
zwitterionic characteristics of glycine. Surface adsorbed H atoms
and/or direct electron transfer might result in step-wise reduction
of the depositing metals.
[0236] In 2004, Zhang et al. [J. Zhang, P. Evans, and G. Zangari ,
J. Magn. Magn. Mater., 283, 89, (2004).] used the plating solution
proposed by Schwartz et al. [N. V. Myung, M. Schwartz, and K. Nobe,
in Fundamental Aspects of Electrochemical Deposition and
Dissolution, M. Matlosz, D. Landolt, R. Aogaki, Y. Sato, and J. B.
Talbot, Editors, PV 99-33, p. 263, The Electrochemical Society
Proceedings Series, Pennington, N.J. (1999).] to synthesize Sm--Co
nanoparticles by single short pulse electrodeposition. Nanoparticle
composition was a function of pulse amplitude (PCD 0.1-1.5
A/cm.sup.2) and pulse duration (T.sub.on 5-100 ms); the relative
atomic percent of Sm, defined as Sm/(Sm+Co), increased with
increasing PCD and decreasing T.sub.on XRD and XPS data indicate
that hcp Co--Sm metallic alloys mixed with metal oxides have been
obtained. The oxygen atomic ratio O/(Sm+Co+O) was a function of
T.sub.on. Increasing T.sub.on decreased Sm content, while oxygen
content increased up to a maximum of about 50 at %. For short
T.sub.on (few ms), oxygen content was as low as 3 at % (PCD=1000
mA/cm.sup.2). In-plane coercivities up to 5.3 kOe have been
achieved for as-plated nanoparticles for Sm content of about 20 at
%.
[0237] D. Applications of Magnetic Co--Sm Alloys
[0238] In one aspect, the disclosed method and compositions can be
used in connection with high performance nanostructured permanent
magnets including high temperature applications in aeronautical and
aerospace applications. In a further aspect, the disclosed method
and compositions can be used to produce dramatically miniaturized
devices including electric motors, generators, actuators,
alternators, gyros, magnetic couplings, magnetic bearings,
centrifuges, hearing aid devices, computer hard drives, camcorders,
industrial robots, maglev trains, and magnetic imaging systems
(MIS).
[0239] In a yet further aspect, the disclosed method and
compositions can be used to produce thick film (>1 nm)
deposition for microelectromechanical systems (MEMS) devices.
[0240] In a still further aspect, the disclosed method and
compositions can be used to produce ultra thin (<100 nm)
controlled electrodeposition for nano-electromechanical systems,
and nanosize biomedical devices and neuroelectrochemical
applications.
[0241] E. Aqueous Electrodeposition Compositions
[0242] In one aspect, the invention relates to compositions for
enhancing the aqueous electrodeposition of rare earth-transition
metal alloys comprising: a water soluble salt of samarium, a water
soluble salt of cobalt, and a comlexant. In a further aspect, the
water soluble salt of samarium is samarium sulfamate. In a further
aspect, the water soluble salt of cobalt is cobalt sulfate or
cobalt sulfamate. In a further aspect, the composition comprises
one or more supporting electrolytes. In a further aspect, the
composition further comprises boric acid. In one aspect, the
electrodeposition can be performed onto a conducting (e.g., metal)
substrate.
[0243] In one aspect, the complexant can be one or more amino acid.
The amino acid can be any amino acid known to those of skill in the
art. In a further aspect, the amino acid is selected from amine
carboxylates, for example, glycine, alanine, and serine,
[0244] In a further aspect, the complexant can be one or more
hydroxycarboxylic acid. The hydroxycarboxylic acid can be any
hydroxycarboxylic acid known to those of skill in the art. In a
further aspect, the hydroxycarboxylic acid is selcted from malic,
glycolic and lactic acids, citric, and tartaric acids.
[0245] In one aspect, the one or more supporting electrolytes
(e.g., conducting salts) can be any electrolytes known to those of
skill in the art. In a further aspect, the one or more electrolytes
are selected from ammonium sulfamate, ammonium sulfate, ammonium
chloride, and mixtures thereof.
[0246] In one aspect, the composition can comprise from about 0.25M
to about 2.0M of the water soluble salt of samarium, from about
0.01M to about 0.5M of the water soluble salt of cobalt, from about
0.05M to about 0.5M of the complexant, and from about 0.1M to about
3M of the supporting electrolyte. In a further aspect, the
composition can comprise 1M of the water soluble salt of samarium,
0.05M of the water soluble salt of cobalt, 0.15M of the complexant,
and 1M of the supporting electrolyte.
[0247] In one aspect, the water soluble salt of samarium is
samarium sulfamate. In one aspect, the water soluble salt of cobalt
is cobalt sulfate or cobalt sulfamate. In one aspect, the
complexant is an amino acid, for example, glycine. In one aspect,
the complexant is a hydroxycarboxylic acid, for example, malic or
citric acid. In one aspect, the conducting salt is ammonium
sulfamate. In a further aspect, the water soluble salt of samarium
is samarium sulfamate, the water soluble salt of cobalt is cobalt
sulfate or cobalt sulfamate, the complexant is glycine, and the
supporting electrolyte is ammonium sulfamate.
[0248] It is understood that the disclosed compositions can be used
in connection with the disclosed methods.
[0249] F. Electrodeposition Methods
[0250] In one aspect, the invention relates to methods for
electrodepositing a samarium-cobalt coating onto a conducting
(e.g., metal) substrate, comprising placing an aqueous solution
containing a water soluble salt of samarium, a water soluble salt
of cobalt, one or more supporting electrolytes, and a comlexant
into a plating bath, placing an anode and the substrate to be
coated into the bath and connecting the anode and the substrate to
a power supply, with the substrate acting as the cathode, adjusting
the pH of the bath to a suitable operating level, and applying a
direct current through the anode and substrate causing the samarium
and the cobalt to migrate to, and adhere to, the substrate. In one
aspect, the aqueous solution further comprises boric acid.
[0251] In one aspect, the method can further comprise an annealing
step.
[0252] In one aspect, the complexant can be one or more amino acid.
The amino acid can be any amino acid known to those of skill in the
art. In a further aspect, the amino acid is selected from amine
carboxylates, for example, glycine, alanine, and serine,
[0253] In a further aspect, the complexant can be one or more
hydroxycarboxylic acid. The hydroxycarboxylic acid can be any
hydroxycarboxylic acid known to those of skill in the art. In a
further aspect, the hydroxycarboxylic acid is selcted from malic,
glycolic and lactic acids, citric, and tartaric acids.
[0254] In one aspect, the one or more supporting electrolytes
(e.g., conducting salts) can be any electrolytes known to those of
skill in the art. In a further aspect, the one or more electrolytes
are selected from ammonium sulfamate, ammonium sulfate, ammonium
chloride, and mixtures thereof.
[0255] In one aspect, the aqueous solution can comprise from about
0.25M to about 2.0M of the water soluble salt of samarium, from
about 0.01M to about 0.5M of the water soluble salt of cobalt, from
about 0.05M to about 0.5M of the complexant, and from about 0.0001M
to about 3M of the supporting electrolyte. In a further aspect, the
aqueous solution can comprise about 1M of the water soluble salt of
samarium, about 0.05M of the water soluble salt of cobalt, about
0.15M of the complexant, and about 1M of the supporting
electrolyte.
[0256] In one aspect, the water soluble salt of samarium is
samarium sulfamate. In one aspect, the water soluble salt of cobalt
is cobalt sulfate or cobalt sulfamate. In one aspect, the
complexant is an amino acid, for example, glycine. In one aspect,
the complexant is a hydroxycarboxylic acid, for example, malic or
citric acid. In one aspect, the supporting electrolyte is ammonium
sulfamate. In a further aspect, the water soluble salt of samarium
is samarium sulfamate, the water soluble salt of cobalt is cobalt
sulfate or cobalt sulfamate, the complexant is glycine, and the
supporting electrolyte is ammonium sulfamate.
[0257] In one aspect, a current density of from about 5 mA/cm.sup.2
to about 600 mA/cm.sup.2 is applied across the anode and cathode.
In various aspects, the current density can be, for example, from
about 5 mA/cm.sup.2 to about 300 mA/cm.sup.2, from about 5
mA/cm.sup.2 to about 100 mA/cm.sup.2, from about 5 mA/cm.sup.2 to
about 50 mA/cm.sup.2, from about 5 mA/cm.sup.2 to about 20
mA/cm.sup.2, from about 10 mA/cm.sup.2 to about 300 mA/cm.sup.2,
from about 10 mA/cm.sup.2 to about 100 mA/cm.sup.2, from about 10
mA/cm.sup.2 to about 50 mA/cm.sup.2, from about 10 mA/cm.sup.2 to
about 20 mA/cm.sup.2, from about 0 mA/cm.sup.2 to about 300
mA/cm.sup.2, from about 0 mA/cm.sup.2 to about 100 mA/cm.sup.2,
from about 0 mA/cm.sup.2 to about 50 mA/cm.sup.2, or from about 0
mA/cm.sup.2 to about 20 mA/cm.sup.2. In a further aspect, the DC
current density is a DC current density. In a further aspect, the
current is an alternating current. In a further aspect, the current
is a pulsed current. In a further aspect, the current is applied
with pulse current modifications varying with duty cycle and
frequency.
[0258] In one aspect, the pH of the solution is from about 3 to
about 6. In a further aspect, the pH of the solution is adjusted to
from about 4 to about 6.5. In a further aspect, the pH of the
solution is about 4.
[0259] In one aspect, the electrodeposition is conducted at a
temperature of from grater than about 0.degree. C. to less than
about 100.degree. C. In a further aspect, the electrodeposition is
conducted at a temperature of from about 20.degree. C. to about
80.degree. C. In a further aspect, the electrodeposition is
conducted at a temperature of from about 20.degree. C. to about
60.degree. C. In a further aspect, the electrodeposition is
conducted at a temperature of from about 20.degree. C. to about
40.degree. C. In a further aspect, the solution temperature is from
about 25.degree. C. to about 60.degree. C., for example, about
25.degree. C., about 40.degree. C., or about 60.degree. C. In a yet
further aspect, the electrodeposition is conducted at about room
temperature.
[0260] The electrodeposition can be conducted with stirring. In a
further aspect, the electrodeposition is conducted without
stirring. In a further aspect, the electrodeposition is conducted
with oscillatory stirring. In a further aspect, the
electrodeposition is conducted with oscillatory stirring at a rate
of from about 40 to about 60 cycles/min, for example, about 48
cycles/min.
[0261] It is understood that the disclosed compositions can be used
in connection with the disclosed methods.
[0262] Also disclosed are samarium-cobalt coatings produced by the
disclosed methods.
[0263] G. Nanostructured Magnetic Coatings
[0264] In one aspect, the invention relates to nanostructured
magnetic coatings comprising a magnetic alloy of a rare earth metal
and a transition metal. In a further aspect, the coatings are
electrodeposited. In a further aspect, the coatings are
electrodeposited from aqueous solution.
[0265] In one aspect, the rare earth metal is samarium. In one
aspect, the transition metal is cobalt. In a further aspect, the
rare earth metal is samarium and transition metal is cobalt. In a
further aspect, the alloy comprises SmCo.sub.5 or
Sm.sub.2Co.sub.17.
[0266] In certain aspects, the electrodeposited alloy contains
sufficient samarium content to perform as a precursor to forming
magnetic SmCo.sub.5 and/or Sm.sub.2Co.sub.17.
[0267] It is understood that the disclosed nanostructured magnetic
coatings can be produced using the disclosed methods and
compositions.
[0268] H. Experimental
[0269] The following examples are put forth so as to provide those
of ordinary skill in the art with a complete disclosure and
description of how the compounds, compositions, articles, devices
and/or methods claimed herein are made and evaluated, and are
intended to be purely exemplary of the invention and are not
intended to limit the scope of what the inventors regard as their
invention. Efforts have been made to ensure accuracy with respect
to numbers (e.g., amounts, temperature, etc.), but some errors and
deviations should be accounted for. Unless indicated otherwise,
parts are parts by weight, temperature is in .degree. C. or is at
ambient temperature, and pressure is at or near atmospheric.
[0270] 1. Aqueous Electrodeposition of Rare Earth Metals and
Transition Metals
[0271] Rare earth (e.g., samarium) and transition metal (e.g.,
cobalt) elements can be electroplated out of an aqueous solution to
form bright metallic coatings on substrates by proper selection of
the additives, such as complexing agent, solution pH, operating
temperature, current density, complexing agent/metal ratio,
complexing agent/transition metal ratio, and duty cycle.
Particularly suitable complexing agents are glycine, alanine, and
serine, which are all amino acids with a single carboxyl group.
With the exception of cysteine, complexing agents evaluated which
were not effective were amino acids with more than one carboxyl
group or were not amino acids. Cysteine is an amino acid with one
carboxyl group and a thio- group (--SH). The --SH apparently
interfered with obtaining the desired result by causing the
formation of hydroxides under the conditions evaluated.
[0272] While varying the operating conditions resulted in lesser
concentrations of the desired materials in the films produced,
conditions were still suitable for preparing RE containing
coatings. The preferred complexing agent is glycine but other
aminecarboxylates were also found to be effective. The preferred
operating conditions include a current density of at least 5
mA/cm.sup.2, room temperature, a pH of 4, and a Co/glycine ratio of
about 0.3. However, it has been found that addition of NH.sub.4Cl
to the processing bath sharply reduced hydrogen evolution resulting
in higher RE content deposits. Furthermore, while a pH of 4 is
preferred, metallic deposits were obtained over a wide pH range
including pH less than 4 and greater than 7. Stable alkaline
plating baths for RE and TM salts are disclosed.
[0273] Plating solutions can be prepared containing various
complexing agents, and transition metals (TM) (e.g., Co, Fe, Ni)
and rare earth chloride salts. The solution pH can be adjusted
upward with NaOH and lowered with HCl. Electrodeposition can be
carried out at room temperature (RT) with DC current in the
solutions containing TMCl.sub.2 and La, Ce, Nd and a rare earth
mixture (MOLYCORP.TM.) referred to below as the REM mixture. Other
commercial rare earth mixtures are also suitable. The composition
of the Molycorp.TM. mixture is given in Table 2.
TABLE-US-00002 TABLE 2 Rare Earth Mixture (Molycorp .TM.) Analysis
Equivalent Wt. Percent Element % as oxide % as carbonate Metal Ce
1.0 1.3 0.7 La 45.9 64.4 39.2 Nd 12.9 18.0 11.1 Pr 4.8 6.7 3.9 Sm
0.4 0.6 0.3 Gd 0.3 0.4 0.3 Y 0.3 0.5 0.2 other RE ~0.4 ~0.6 ~0.4
other elements ~0.1 ~0.2 --
[0274] Primary test solutions were (A) Bath A--0.12M TMCl.sub.2,
0.5M B(OH).sub.3, 0.36M complexing agent, 0.3 M RE or REM (B) Bath
B--same as Bath A+1M NH.sub.4 Cl.
[0275] Solutions were either unstirred or stirred using a magnetic
stirrer or by oscillatory stirring (48 cycles/min).
[0276] Each solution was used until accumulative exposure of
240-A-min/L at which point a new solution was prepared. The
solution becomes less effective after 240-A-min/L because of
consumption of the key ingredients in the rare earth mixture used.
Brass or stainless steel panels were used as substrates. The
substrates were mechanically cleaned and then subjected to a
chemical treatment including soaking in alkaline cleaning solution
for 10 min followed by rinsing with deionized water. Surfaces were
then activated just before electrodeposition by immersion in 10%
HCl for 30 sec. Soluble Co, Fe, or Ni anodes were used, depending
on the solution, to minimize changes in the metal solution
composition and to avoid known side effects due to insoluble
anodes.
[0277] A Kraft Dynatronix power supply (model DRP 20-5) was used to
provide pulse current (PC) waveforms and a PAR
potentiostate/galvanostat (model 173) was used to provide DC
current.
[0278] In order to evaluate the efficiency of the electrodeposition
of RE-TM materials from solutions containing complexing agents,
nitric acid was used to dissolve the deposited films. After
evaporating the nitric acid solution to dryness, the resultant
dried RE-TM residue was dissolved with deionized water and
transferred to a plastic test tube. Hydrofluoric acid was added to
separate the rare earths from ferrous metals by precipitation of
rare earths fluorides. The precipitate was thoroughly washed with
deionized water and transferred to a 50 milliliter beaker. Boric
acid and nitric acid were then added to dissolve the precipitated
rare earth fluorides. The solution was evaporated to dryness,
resulting in water-soluble rare earth compounds. The dried sample
was redissolved with deionized water and transferred into a 10
milliliter volumetric flask. One milliliter of ammonium acetate
buffer and a complexing agent (alizarin red) were added. Ammonium
acetate was used to buffer the solution to pH of 4.7 and the
alizarin red was complexed with the rare earth to develop a
specific color. After dilution to 10 milliliters, a
spectrophotometer (.lamda.=530 nm) was used to measure the
absorbance. The absorbance obtained was then used to estimate the
amount of rare earth in the deposit.
[0279] For plating solutions free from complexing agents,
precipitation by oxalic acid was followed by dissolution of the
oxalate precipitate with concentrated hydrocholoric acid, and
finally precipitation with ammonia. The final white hydroxide
precipitate from the ammoniacal solutions confirmed the presence of
lanthanons in the deposit.
[0280] a. Effects of Complexing Agents
[0281] Using Bath A, eleven (11) complexing agents were
investigated to study their effects on the production of RE-Co
deposits and the stability of solutions. The solutions were stirred
and exposed to current density of 20 mA/cm.sup.2 unless. The
results are summarized in Table 3.
TABLE-US-00003 TABLE 3 Effects of Complexing Agent* Rare Earth
Content Additives in Deposit Appearance Glycine (REM) 8.0% Bright
metallic Glycine (Ce) 6.3% Grey metallic Glycine (La) 7.5% Black
metallic Glycine (Nd) 3.4% Gray metallic Alanine (REM) 3.8% Bright
metallic Serine (REM) 5.0% Bright metallic Aspartic acid (REM) Not
analyzed Non-metallic white (RE) hydroxide Glutamic acid (REM) Not
analyzed Non-metallic white (RE) hydroxide Malic acid (REM) No RE
Grey metallic (pH 8.5) Cysteine (REM) Not analyzed Non-metallic
hydroxide Glycolic acid (REM) 0.2-1% Bright metallic Lactic acid
(REM) 0.2-1% Bright metallic EDTA (REM) No deposit *Solutions (Bath
A, pH 4) were stirred and electrodeposition was at 20
mA/cm.sup.2
[0282] It was found that the a-amino acids, glycine, alanine and
serine stabilized the plating solution at pH 4, resulting in
metallic deposits containing rare earths. The highest RE content in
deposited films was obtained in solutions containing glycine while
deposits of lower RE content were obtained with alaline and serine.
All the deposits exhibited bright metallic appearance, which
differed from the typical matte appearance of cobalt
electrodeposits, indicating the effect of the rare earth elements.
In order to test which element was preferentially deposited from
the REM, separate runs were performed in the solutions containing
glycine and Ce(Cl).sub.3, Nd(Cl).sub.3 or La(Cl).sub.3. The
presence of lanthanum in the solution gave a black metallic deposit
containing 7.5% lanthanum, 3.4% Nd was obtained with NdCl.sub.3 and
these Ce(Cl.sub.3) produced a gray metallic deposit with a 6.4% Ce
in the films. In these cases, the 3 RE content of the deposit was
lower than that when the RE mixture (8%) was used.
[0283] Solutions containing aspartic acid and glutamic acid were
not stable and produced uniform white precipitates which consisted
of RE hydroxides instead of metal films. Black deposits were
obtained from the solutions containing cysteine and those cysteine
solutions were also not stable.
[0284] The solutions containing glycolic acid or lactic acid were
cloudy at pH4 due to the formation of small amounts of hydroxides.
However, bright metallic deposits containing small amounts of RE
were obtained from filtered solutions. EDTA formed strong complexes
with Co. As a result, no deposits were obtained from the EDTA
containing solutions.
[0285] In addition to the results shown in Table 3, a Nd--Ni
deposit of 6% Nd was obtained from Bath B using ethylene diamine as
a complexing agent. The solution (pH5) was unstirred and deposits
were obtained at 15 mA/cm.sup.2.
[0286] b. Effect of Direct Current Deposition
[0287] To evaluate the effect of current density on resultant
deposits, electrodeposition was carried out at room temperature and
current densities of 5, 10, and 20 mA/cm.sup.2 for Co-RE, Ni-RE and
Fe-RE solutions containing glycine at pH4. The solution contained
0.12M (Fe, Ni, Co) Cl.sub.2, 0.5M B(OH).sub.3, 0.36M glycine and
0.3 RE (La, Ce, Nd), or REM. FIG. 11 compares the dependence of the
rare earth content (% rare earth) of the deposited films at
different current densities. Generally, the percentage of rare
earth in the film increased with increasing current density.
Deposit content of the rare earths were greater in Ni alloys, less
in Fe alloys and least in Co alloys. Rare earth deposit contents
are typically greatest from unstirred solutions, a lesser amount
from solutions mixed by oscillatory stirring and least from more
vigorous agitation with a magnetic stirrer. Thus, mass transfer
effects can be important in the efficacy of RE-TM
electrodeposition.
[0288] C. Effect of Temperature
[0289] Electrodeposition from magnetic stirred Bath A containing
CoCl.sub.2 and the rare earth mixture (REM) was run at both room
temperature and 65.degree. C. to examine the temperature dependence
of Re--Co deposits. It was found that at the same current density
(20 mA/cm.sup.2), the rare earth in the deposits at 65.degree. C.
was .about.3%, which was less than half the 6.6% obtained at room
temperature. Thus, the cobalt deposition rate is greatly enhanced
and the RE deposition reduced as temperature is increased. In other
words, a lower temperature during electrodeposition favors RE
deposition.
[0290] d. Effect of Complexing Agent to Metal Ratio
[0291] The ratio of the glycine concentration to metal
concentrations in magnetic stirred solutions also had a measurable
effect on RE-Co electrodeposition. FIG. 12 shows the effects of
glycine/Co solution ratios with CoCl.sub.2 held constant at 0.12M
on the deposit RE content obtained at room temperature with a
current density of 20 mA/cm.sup.2 and a pH of 4. There appears to
be a plateau or an approach to a maximum in deposited RE content as
the glycine/Co ratio approached 1. At glycine/Co ratio>1, a
sharp decrease in the deposit RE content with increasing ratios was
observed (FIG. 12).
[0292] e. Effect of Co(Cl).sub.2+Glycine
[0293] In this study, the magnetic stirred solution RE
concentration was maintained constant at 0.3M while the combined
concentrations of Co(Cl).sub.2+glycine was increased at a constant
ratio: 1Co:3glycine. FIG. 13 shows increased Co(Cl).sub.2+glycine
concentrations resulted in decreased deposit RE content. At a
combined total concentrations of 1.5M, practically no RE was
deposited indicating the possible inhibitory-effect of increasing
addition agent concentrations. Again, operating conditions were
room temperature, pH of 4 and a current density of 20
mA/cm.sup.2.
[0294] The duty cycle for PC electrodeposition is defined as
t.sub.on/(t.sub.on+t.sub.off), and the average current density is
the peak current density times the duty cycle. Pulsed current
deposition of RE-Co alloys was performed at an average current
density of 20 mA/cm.sup.2 with T.sub.on at 5 msec. FIG. 14 shows
that the deposit RE content was fairly constant at .about.4.5.+-.5%
at duty cycles from 0.1 to 0.8. In this range, the peak cathodic
current densities ranged from 200 to 25 mA/cm.sup.2, along with
decreasing off-times of 45 to 1.75 msec, respectively. At duty
cycles greater than 0.8, approaching DC plating, the deposit RE
content increased to .about.6.+1% and was similar to that obtained
with constant DC current.
[0295] As the peak cathodic current density increased, the required
longer off-times (relaxation times) permitted sufficient diffusion
of either or both the Co or RE species into the cathode diffusion
layer. However, at any peak cathodic current density greater than
DC, the diffusion of the RE was insufficient to provide the
necessary replenishment, resulting in lower deposit content,
although the bulk solution concentration was three times that of
cobalt. More Co deposited during the on-time indicating either fast
deposition rates or mass transfer compared to the RE.
[0296] For Co--Re deposition, deposit RE content was relatively
constant with PC deposition up to duty cycle of 0.8 and then
increased at higher duty cycle. DC electrodeposition gave the
highest amount of RE in the films. Temperatures greater than room
temperature increased additive to metal ratio, and increased cobalt
concentration resulted in lower RE in the films.
[0297] f. Effect of Solution Ph and NH.sub.4Cl
[0298] The solution pH can be important to the electrodeposition
process. The pH can affect the onset of the hydrogen evolution
reaction, the composition of the deposits, the current efficiencies
and the stability of the solution. Addition of NH.sub.4Cl to Bath A
was an effort to lessen the rate of hydrogen evolution. FIG. 15
illustrates the interdependence of current density with solution pH
on the composition of deposits obtained from TM-Nd-glycine
solutions. In general, the deposit Nd content increased fairly
linearly with increasing current density and increasing solution pH
in the range of 5-40 mA/cm.sup.2 and pH4-5.4, respectively, the
exception being Nd--Ni deposits which exhibited a maximum deposit
content at 10 mA/cm.sup.2 and solution pH of 4.8.
[0299] It was observed that the presence of NH.sub.4Cl
significantly decreased hydrogen evolution during electrodeposition
of RE-TM alloys. As a result the pH range to obtain metallic
deposits was increased. For example, 29% Ce in Ce--Ni deposits were
obtained with glycine @ pH2.7 and 15 mA/sq.cm (Bath B) and 23% Nd
was obtained in Nd--Ni deposits with alanine)@pH7 and 20 mA/sq.cm
(Bath B). Furthermore, deposit RE content was generally higher in
solutions containing NH.sub.4Cl. For example, for Ce--Ni deposits
at 5 and 20 mA/cm.sup.2 with oscillatory stirring (Bath B), Ce
contents were 10.5% and 22.5%, respectively. In comparison 8.2% and
16.2% were obtained from Bath A.
[0300] g. Mass Transfer Effects
[0301] The degree of solution agitation during electrodeposition of
RE-TM alloys can have an effect on the RE content of the deposits.
FIG. 16 shows that the Ce content in Ce--Ni deposits was less from
oscillatory stirred solutions (48 cycles/min) compared to unstirred
solutions. Further, RE deposit contents were even lower from
solutions agitated more vigorously using a magnetic stirrer. On the
other hand, visual inspection of the deposits indicates that
solution agitation improved the quality (appearance) of the
deposits. For the electrodeposition of bright metallic or ferrous
metal-RE alloys, the most effective complexing agents appear to
include glycine, alanine and serine. These complexing agents are
amino acids with a specific chemical structure, namely a single
carboxyl group and thus differ chemically from the other sampled
complexing agents which were not found to be suitable. Therefore,
it would appear that other amino acids with single carboxyl groups
would be suitable compounds to create the same result under similar
operating conditions and solution compositions. Other types of
complexing agents investigated were either not as effective or
ineffective, usually resulted in precipitation of hydroxide in the
solution and/or in the deposited films or prevented deposition of
the RE or resulted in unacceptable appearing films.
[0302] 2. Hull Cell Studies
[0303] Co--Sm permanent magnets, such as Sm.sub.2Co.sub.17 and
SmCo.sub.5, require 10.53 and 16.67 at % Sm content, respectively.
To satisfy the composition requirements of Co--Sm magnets, the
alloys produced by electrodeposition must contain enough Sm
content. Therefore, high Sm content Co--Sm alloys electrodeposited
from aqueous solution is the initial goal of this research.
[0304] An electrodeposition process can be operated successfully
only when the key parameters are properly controlled. These are
components and compositions of plating baths (e.g. metal ions,
supporting electrolytes and additives) and operating conditions
(e.g. current density (CD), solution temperature, pH, fluid
dynamics and current waveforms). To obtain high Sm deposit content,
these parameters need to be studied carefully.
[0305] The Hull cell is an effective screening device often used by
electroplaters to solve problems of the electroplating process. The
Hull cell has been recognized as a powerful tool to study the
approximate deposit properties. Generally, the Hull cell provides
information regarding the deposit characteristics over a wide range
of CDs and multiple experimental results in a single experiment.
For its high efficiency, Hull cell technology was chosen to
determine the dependence of Sm deposit content on deposit
parameters and coupling between deposit parameters in the
electrodeposition of Co--Sm alloys. Although the result by the Hull
cell is less accurate and more limited than by parallel electrodes,
it still provides a good approximation to the trends in Sm deposit
content by varying the electrodeposition parameters in the initial
investigations of the electrodeposition of Co--Sm alloys.
[0306] FIG. 17 shows the flowchart of a Hull cell experiment which
mainly includes four parts: pretreatment of cathode, DC or PC
electrodeposition, post-treatment of specimen and characterization.
Fundamentals, definitions, experimental setup, design of Hull cell
study, pretreatment and post-treatment, and characterization and
analysis of the specimens will be described in the following
discussion.
[0307] a. Fundamentals of the Hull Cell
[0308] The Hull cell, developed by R. O. Hull [R. O. Hull, U.S.
Pat. No. 2,149,344 (1939)], is a miniature trapezoidal plating cell
(267 mL vol) which provides a current density (CD) range on the
cathode test panel, depending on the applied current. FIG. 18 shows
Hull cell cathode test panel at the right end (point b), having the
longest cathode-anode distance (D.sub.b), resulting in the lowest
CD; the CD continuously increases as the current path along the
cathode decreases and reaches a maximum at point a, the shortest
cathode-anode distance (D.sub.a).
[0309] Thus, it is universally used as an economical screening
device to evaluate the effects of solution compositions and applied
operating conditions on the deposit appearance, composition and
crystal structure as a result of incremental CDs on a single
cathode surface, especially for initial investigations of alloy
electrodeposition. Further, deposits on selected portions of the
test panel can be analyzed by energy dispersive spectroscopy (EDS)
and X-ray diffraction (XRD) to provide additional information
regarding compositions and crystal structures. The current density
at which the deposit no longer has a metallic appearance, referred
to as "burnt" by practicing electroplaters, was defined as the
maximum current density (CD.sub.max) for a particular plating
system.
[0310] To minimize solution concentration and temperature gradients
during electrodeposition, the Hull cell was equipped with a
motorized slide mechanism with an attached paddle located alongside
the cathode providing a reciprocal horizontal motion (agitation)
with a sweep rate of 80 cycles/min, regulated by a variable
resistor.
[0311] Hull developed an equation describing the CD distribution on
the test panel for a typical 267 mL Hull cell:
CD=I(27.7-48.7 log L)A/ft.sup.2 (ASF) (Equation 6)
where I is the applied current in amperes, and L is the position on
the test panel in inches from the low CD end (point b). This
equation was derived basing on the standard 10.times.5 cm (area=50
cm.sup.2) Hull cell panel. The design of the Hull cell allows us to
obtain deposits at different CDs on a single substrate. In other
words, it saves a lot of time by providing a spectrum (Hull cell
pattern) of a deposit obtained at continuous changing CD along its
length on a single panel. The deposits can then be analyzed to
determine properties at a particular CD.
[0312] However, the design of the Hull cell is based on primary
current density distribution neglecting the secondary density
distribution [L. J. Durney, Electroplating Engineering Handbook
(4th edition), Van Nostrand Reinhold Company Inc., Taiwan, (1984),
pp. 461-473] due to the depletion of metal ions at cathode surface
during the electrodeposition. The apparent CDs on the test panel,
as calculated with Equation 6, only provide an approximation of the
"true" CDs. Therefore, the analysis in Hull cell only shows the
trends rather than the precise values of deposit properties changed
by electrodeposition parameters. Only Sm deposit contents (by EDS)
and crystal structures (by XRD) were analyzed in the Hull cell
test. In addition, analysis of the deposit at CD.sub.max is
difficult to determine because cutting a piece of specimen at
CD.sub.max non-metallic deposits at CDs slightly higher than
CD.sub.max were included. Compared to the result by parallel
electrodes depositions, the Hull cell result is less accurate and
more limited. Although the Hull cell has these drawbacks, it is
still an efficient device providing a good approximation of trends
for the preliminary investigation of the electrodeposition of
Co--Sm alloys.
[0313] b. Definitions and Parameters
[0314] DC&PC electrodeposition: Metallic deposit is defined as
a deposit with a visual metallic-appearance, Sm content (at %) is
defined as the atomic percentage of Sm in deposited total metals,
Sm content
( at % ) = Sm total metals ( at % ) = Sm Sm + Co ( at % )
##EQU00001##
[0315] DC electrodeposition: CD is the current density defined as
current per unit deposit area, CD.sub.max, is defined as the
highest CD to obtain metallic-appearing deposits.
[0316] PC electrodeposition: PCD is peak current density defined as
the maximum CD in one complete pulse cycle, PCD.sub.max is defined
as the highest PCD to obtain metallic appearing deposits, T.sub.on,
is the time duration of the on-current in one complete pulse cycle,
T.sub.off is the time duration of the off-current in one complete
pulse cycle, Period is the time duration for one complete cycle,
period=T.sub.total=T.sub.on+T.sub.off, Frequency (f) is defined as
the number of complete cycles per second,
f = 1 period = 1 T on + T off ##EQU00002##
[0317] Duty cycle (.gamma.) is defined as the ratio of T.sub.on to
period,
.gamma. = T on T on + T off = T on f ##EQU00003##
[0318] c. Experimental Setup and Design
[0319] The setup for Hull cell electrodeposition is shown in FIG.
20. A Kraft Dynatronix power generator (model DRP 20-5-10) served
as power source to supply current needed for DC and PC
electrodeposition, a coulometer to measure the total charge passed,
and an oscilloscope to monitor the waveform during pulse current
electrodeposition. Masked brass panels (10.times.5 cm) with exposed
15 cm.sup.2 (10.times.1.5 cm) deposit area for DC and with 7.5
cm.sup.2 (10.times.0.75 cm) for PC electrodeposition served as
cathodes and a platinum sheet (5.times.5 cm) was used as the
anode.
[0320] The reduction of deposit area from 50 cm.sup.2 (whole brass
panel) to 15 cm.sup.2 (DC) or 7.5 cm.sup.2 (PC) increased the CD
range for the parametric studies. Therefore, equation 1 was
modified by using 15 cm.sup.2 (or 7.5 cm.sup.2) deposit area:
CD=I(85.8.-150.8 log L), mA/cm.sup.2 (4.5 A/15 cm.sup.2) (Equation
2)
CD=1(171.6.-301.610 log L), mA/cm.sup.2(4.5 A/7.5 cm.sup.2)
(Equation 3)
where 1 is the total applied current in amperes, and L is the
position on the test panel in inches from the low CD end (right
end).
[0321] The deposits were obtained in a 267 mL Hull cell filled with
the plating baths as shown in Table 4.
TABLE-US-00004 TABLE 4 Plating baths used in Hull cell studies Bath
# Sm sulfamate Co sulfate Glycine NH.sub.4 Sulfamate pH 1 1 M 0.05
M 0.15 M 5.7 2 1 M 5.8 3 1 M 0.15 M 5.7 4 0.05 M 5.6 5 0.05 M 0.15
M 4.5 6 1 M 0.05 M 5.9 7 1 M 0.05 M 3 M 4.0 8 1 M 0.05 M 0.15 M 1 M
5.9 *The pH values of the plating baths were measured at 25.degree.
C.
[0322] Bath 1 was used to study the effect of CD and temperature;
baths 2 and 3 were used to study the effect of glycine on the
formation of Sm oxide and hydroxide; baths 4 and 5 were used to
study the effects of glycine on the electrodeposition of Co; baths
1, 6 and 7 were used to study the effect of the glycine
concentration on the codeposition of Sm and Co; baths 1 and 8 were
used to study the effect of ammonium sulfamate, as the supporting
electrolyte.
[0323] Unless otherwise noted, the total charge passed was 100
coulombs for DC and 50 coulombs for PC electrodeposition to provide
deposits thick enough to be analyzed. The deposit area was 15
cm.sup.2 for DC and 7.5 cm.sup.2 for PC electrodeposition. The
applied charge density remained constant as 6.67 C/cm.sup.2 for
both DC and PC. The applied current was 4.5 A for DC (25 and
60.degree. C.) and for PC at 25.degree. C. and 7A at 60.degree. C.
providing a wide range of CDs. Solutions were not agitated during
electrodeposition.
[0324] (1) Pretreatment and Post-Treatment
[0325] Before electrodeposition, the brass panels were mechanically
cleaned with a brush, soaked in 0.1M NaOH for 10 min., rinsed in
deionized water, immersed in 10% HCl for 30 seconds and then rinsed
with deionized water.
[0326] After the Co--Sm alloy was deposited for 100 coulombs in DC
or 50 coulombs in PC, deposits were removed from the plating
solution, rinsed with deionized water, and then dried with nitrogen
gas. Disk-shaped specimens of diameter of 3.2 mm (specimen
area=8.04 mm.sup.2) were die-punched out from deposits for
analysis.
[0327] (2) Characterization and Analysis
[0328] The main purpose of the Hull cell study is to determine the
trend in Sm deposit content by varying the electrodeposition
parameters; the Sm deposit content was determined by energy
dispersive x-ray spectroscopy (EDS) by a Kevex detector within a
Cambridge scanning electron microscopy (SEM) (model Stereoscan
250). A PANalytical X-ray diffraction (XRD) (model X'Pert Pro) was
used to examine crystal structures of deposits by {tilde over
(.THETA.)}2.THETA. scan method. Unless otherwise noted, the
experimental data presented are restricted to metallic-appearance
deposits.
[0329] (3) Energy Dispersive X-Ray Spectrometer (EDS)
[0330] EDS measures the energy and intensity distribution of X-rays
generated by the bombardment of electron beam on the specimen. The
composition of the specimen can be obtained by comparing the peak
intensities of Co (K.sub..alpha.1, 6.93 ev) and Sm (L.sub..alpha.1,
5.62 ev) to the intensities of the internal standard of pure Co and
Sm, respectively, to get the k'-ratios
( k ' = I specimen i I pure element i ) ##EQU00004##
then calibrated by ZKF method (a matrix correction technology) to
get the k-ratios of Co and Sm. K-ratios, which are proportional to
the weight percent of elements in the specimens, were used to
obtain the weight and atomic percent of Co and Sm. An example of
energy dispersive spectrum of an electrodeposited Co--Sm alloy is
given in FIG. 21 and the analysis result is shown in Table 5. The
elemental composition in a defined scan area can be easily
determined to a high degree of precision (-0.1 wt. %).
TABLE-US-00005 TABLE 5 Compositional analysis results of an
electrodeposited Co--Sm alloy Element Peak Peak Intensity (cps)
K-Ratio Weight % Atomic % Co K.alpha..sub.1 1793.4 0.8558 85.77
93.89 Sm L.alpha..sub.1 149.2 0.1442 14.23 6.11
[0331] (4) X-Ray Diffraction (XRD)
[0332] XRD [L. V. Azaroff, Elements of X-ray crystallography,
McGraw-Hill, N.Y., (1968)] is a technique in crystallography which
can be used to determine the crystal structures of the specimen by
characterizing its diffraction pattern with Bragg's law. The shape
and size of the unit cell determines the angular position
(2.THETA.) of the diffraction lines; the arrangement of the atoms
within the unit cell determines the relative intensities of the
lines. Information regarding states of Co--Sm alloys (e.g.
crystalline, non-crystalline, intermetallic compound), non-metallic
compounds (e.g., oxide and hydroxide), and prefer orientation (PO)
of deposits can be examined by diffraction peaks. These
characteristics of electrodeposited Co--Sm alloys controlled by
electrodeposition parameters are very useful to study magnetic,
electric and mechanical properties of deposits.
[0333] The grain size of the crystallites in out-of-plane direction
(perpendicular to film plane) can be estimated from the measured
width of their diffraction peaks by Scherrer's formula [B. D.
Cullity and S. R. Stock, Elements of X-ray diffraction (3rd
edition), Prentice Hall, N.J., (2001), p170]:
t = 0.9 .lamda. B Cos ( .theta. B ) ##EQU00005##
where .lamda. is the wavelength of X-ray used to obtain the
diffraction pattern; B is the full-width at half maximum (FWHM),
and .THETA..sub.B is the Bragg's angle of the diffraction peak.
[0334] (5) Effect of Applied Charge, Current and Deposit Area
[0335] As indicated, various applied charges (100 C/15 cm.sup.2 for
DC and 50 C/7.5 cm.sup.2 for PC) and currents (4.5 A/15 cm.sup.2
for DC (25 and 60.degree. C.), 4.5 A/7.5 cm.sup.2 for PC at
25.degree. C. and 7 A/7.5 cm.sup.2 for PC at 60.degree. C.) were
applied to obtain Hull cell patterns. To confirm the results of
CD.sub.max (or PCD.sub.max) obtained at different operating
conditions can be compared, some pre-tests were done as
follows.
[0336] Effect of different applied currents: The purpose of this
test was to evaluate the consistency of PCD.sub.max at various
applied currents. FIG. 22 shows the Hull cell patterns obtained at
60.degree. C. from bath 1 (1M Sm sulfamate, 0.05M Co sulfate, 0.15M
glycine) by PC electrodeposition of applied current of 4.5 and 7 A.
The PCD.sub.max, of 4.5 A was about 990 mA/cm.sup.2 which was close
to the PCD.sub.max of 7 A (about 1000 mA/cm.sup.2). It was
concluded that PCD.sub.max at different applied currents varied
little and the Hull cell patterns obtained at different applied
currents (4.5 and 7 A) can be compared. On the other hand, the
application of current 7 A provided a wider PCD range on Hull cell
patterns obtaining more information of the oxide/hydroxide region
(FIG. 22(b) compared to 4.5 A (FIG. 22(a)). Therefore, a current of
7 A was applied in PC at 60.degree. C. instead of 4.5 A for a wider
PCD range. PCD.sub.max remained unchanged, and Hull cell patterns
obtained at the current of 4.5 and 7 A can be compared.
[0337] Effect of different applied charges: The purpose of this
test was to check the consistency of PCD.sub.max at a fixed charge
density. FIG. 23 shows the Hull cell patterns by PC
electrodeposition at 25.degree. C. from bath 1 for applied
charge/deposit area of 100 C/15 cm.sup.2 and 50 C/7.5 cm.sup.2
(charge density was fixed at 6.67 C/cm.sup.2). The PCD.sub.max of
100 C/15 cm.sup.2 was about 190 mA/cm.sup.2 which was close to the
PCD.sub.max of 50 C/7.5 cm.sup.2 (about 200 mA/cm.sup.2). It was
concluded that as long as the charge density was constant
(charge/deposit area=6.67 C/cm.sup.2), PCD.sub.max varied little.
Therefore, in PC electrodeposition, the PCD.sub.max of Hull cell
patterns obtained at 100 C/15 cm.sup.2 and 50/7.5 cm.sup.2 can be
compared.
[0338] (6) Results and Discussions of DC Electrodeposition
[0339] Effect of current density and solution temperature: Bath 1
(1M Sm sulfamate, 0.05M Co sulfate, 0.15M glycine) was used to
study the effects of current density and solution temperature on
the electrodeposited Co--Sm alloys. The experimental conditions are
shown in Table 6, and their Hull cell patterns in FIG. 24.
TABLE-US-00006 TABLE 6 The effects of current density and solution
temperature [Sm(NH.sub.2SO.sub.3).sub.3] [CoSO.sub.4] T CD.sub.max
EXP # Bath (M) (M) [Glycine] (M) pH (.degree. C.) (mA/cm.sup.2) 3 1
1.00 0.05 0.15 5.7 25 50 6 60 750 45 80 850 * Total charge = 100 C,
applied current = 4.5 A, substrate area = 15 cm.sup.2, pH = 5.7, no
agitation.
[0340] Deposits obtained from bath 1 at 25.degree. C., for example,
showed metallic-appearing for CD below 50 mA/cm.sup.2, burnt
between 50 and 100 mA/cm.sup.2, and white powder at CD above 100
mA/cm.sup.2 (FIG. 24(a)). To characterize these regions, XRD was
used to study their phase compositions. From the result of XRD
patterns of deposit #3 (FIG. 25), the metallic region was
non-crystalline and contained a weak diffraction peak of
Sm(OH).sub.3 (FIG. 25(a)). The burnt region exhibited not only
Sm(OH).sub.3 but also Co(OH).sub.2 and SmO peaks (FIG. 25(b)). The
non-metallic white powder region (FIG. 25(c)) contained
Sm(OH).sub.3, Co(OH).sub.2 and mixtures of Sm and Co oxides.
[0341] Generally, metallic deposits could be obtained only below
critical CD; at higher CDs, non-metallic appearing deposits
containing hydroxides and oxides were obtained. This critical CD
was defined as the maximum current density (CD.sub.max) to obtain
metallic deposits. It was observed that CD.sub.max increased with
increasing solution temperature (Table 6 and FIG. 24). For example,
CD.sub.max increased from 50 to 850 mA/cm.sup.2 by increased
solution temperature from 25 to 80.degree. C. Higher CD resulted in
higher Sm deposit content as shown in FIG. 26. Therefore, high Sm
deposit content of 25 at % can be obtained from bath 1 at
60.degree. C. and 650 mA/cm.sup.2 exceeding the composition
requirement of 16.67 at % for SmCo.sub.5. (Note: The deposit
obtained at 60.degree. C. and 750 mA/cm.sup.2 (CD.sub.max) should
have higher Sm deposit content than at 650 A/cm.sup.2. However, it
was difficult to measure the Sm content at CD.sub.max because it
was too close to the non-metallic region.)
[0342] (7) Effect of Fluid Dynamics
[0343] Bath 1 was used to study the effect of fluid dynamics on
electrodeposition of Co--Sm alloy. Solution agitation was achieved
by a periodic reciprocal movement of the paddle along the Hull cell
panel controlled by a motor (FIG. 27).
[0344] The experimental conditions are provided in Table 7, and the
Hull cell patterns of the deposits are shown in FIG. 28. Solution
agitation didn't significantly affect CD.sub.max (FIG. 28) and Sm
deposit content (FIG. 29) at either 25 or 60.degree. C. To study
mass transfer effect in the electrodeposition of Co--Sm alloy, a
more controlled method, RDE (rotating disk electrode), was used,
and the results are discussed in DC electrodeposition studies.
TABLE-US-00007 TABLE 7 The effect of fluid dynamics
[Sm(NH.sub.2SO.sub.3).sub.3] [CoSO.sub.4] [Glycine] Agitation T
CD.sub.max EXP # Bath (M) (M) (M) (cycles/min) (.degree. C.)
(mA/cm.sup.2) 3 1 1.00 0.05 0.15 0 25 50 9 80 50 6 0 60 750 12 80
750 *Total apply charge = 100 C, applied current = 4.5 A, substrate
area = 15 cm.sup.2 (10 cm .times. 1.5 cm), pH = 5.7.
[0345] (8) Effect of Glycine on the Electrodeposition of Sm and
Co
[0346] Like other RE metals, metallic Sm has not been deposited
from aqueous solution, generally attributed to its very negative
reduction potential [W. M. Latimer, The Oxidation States of the
Elements and Their Potentials in Aqueous Solution, Prentice-Hall,
N.Y., pp. 286-295 (1952)] (E.degree.<-2.3V.sub.SHE). Compared to
Sm, water has a much less negative reduction potential [W. M.
Latimer, The Oxidation States of the Elements and Their Potentials
in Aqueous Solution, Prentice-Hall, N.Y., pp. 29-37 (1952)]
(2H.sub.2O+4e.sup.-.fwdarw.2OH.sup.-+H.sub.2, E.gtoreq.-0.826V).
Typically, hydroxyl ions generated by hydrogen evolution react with
Sm ions to form hydroxides. However, metallic codeposits of Co--Sm
have been obtained from aqueous solutions containing glycine and
its derivatives [L. Chen, M. Schwartz, and K. Nobe, in
Electrodeposited Thin Films, M. Paunovic; M. Schwartz, F. He, N.
Myung, and K. Nobe, in Magnetic Materials, Processes, and Devices
V. Applications to Storage and Microelectromechanical Systems
(MEMS), L. T. Romankiw, S. Krongelb, and C. H. Ahn, Editors, PV
98029, p. 646, The Electrochemical Society Proceedings Series,
Pennington, N.J. (1999); N. V. Myung, M. Schwartz, and K. Nobe, in
Fundamental Aspects of Electrochemical Deposition and Dissolution,
M. Matlosz, D. Landolt, R. Aogaki, Y. Sato, and J . B. Talbot,
Editors, PV 99-33, p. 263, The Electrochemical Society Proceedings
Series, Pennington, N.J. (1999).; M. Schwartz, N. V. Myung, and K.
Nobe, J. Electrochem. Soc., 151, C468, (2004).]. Therefore, it is
of interest to study the effect of glycine on the codeposition of
Co--Sm alloys.
[0347] Various solutions were used to study the effect of glycine
on the formation of samarium oxide and hydroxide (bath 2 and 3),
the electrodeposition of cobalt (bath 4 and 5), and the
codeposition of samarium and cobalt (bath 1, 6 and 7).
[0348] (9) Formation of Sm Oxide and Hydroxide
[0349] Bath 2 (1M Sm sulfamate) and bath 3 (1M Sm sulfamate, 0.15M
glycine) shown in Table 8 were used to study the effect of glycine
on the formation of Sm oxide/hydroxide at 25 and 60.degree. C. FIG.
30 shows the results of the Hull cell patterns.
TABLE-US-00008 TABLE 8 The effect of glycine on formation of Sm
oxide/hydroxide EXP [CoSO.sub.4] [Glycine] T # Bath
[Sm(NH.sub.2SO.sub.3).sub.3] (M) (M) (M) pH (.degree. C.) 41 2 1.00
0 0 5.8 25 42 60 43 3 0.15 5.7 25 44 60 *Total charge = 100 C,
applied current = 4.5 A, substrate area = 15 cm.sup.2, no
agitation.
[0350] Addition of glycine to Sm sulfamate solution did not result
in metallic Sm deposits. However, it seems to play a role to
stabilize Sm ions in solution and reduce the formation of
hydroxides and oxides in deposits. It was noted that a mixture of
Sm hydroxide/oxide was formed when CD reached a critical point;
addition of glycine to the electrolyte decreased the formation of
hydroxides and oxides by extending this critical CD. At 25.degree.
C., for example, the critical CD increased from 60 to 150
mA/cm.sup.2 by addition of 0.15M glycine to 1M Sm sulfamate (FIGS.
30(a) & (b)). Similar results were found at 60.degree. C.
(FIGS. 30(c) & (d)). For solutions with glycine present, higher
CDs were needed to form Sm hydroxide. It has been reported that
glycine derivatives complex Sm ions [J. Torres, C. Kremer, E.
Kremer, H. Pardo, L. Suescun, A. Mombru, S. Dominguez and A.
Mederos , Inorg. Chinn. Acta, 355, 442 (2003); J. Torres, C.
Kremer, E. Kremer, H. Pardo, L. Suescun, A. Mombru, S. Dominguez
and A. Mederos , J. Alloy Comp., 323-324, 119 (2001)] and prevent
the precipitation of Sm(OH).sub.3 [F. Medrano, A. Calderon and A.
K. Yatsimirsky, Chem. Commmun., 1968, (2003)] by complexation of
glycine and Sm ions reducing reaction of Sm.sup.3+ and hydroxyl
ions.
[0351] It was also observed that increasing solution temperature
also depressed formation of Sin hydroxide and oxide without (FIGS.
30(a) & (c)) or with glycine (FIGS. 30(b) & (d)) by
extending the critical CD. In brief, it was found that addition of
glycine and an increase in solution temperature depressed the
formation of Sm oxide and hydroxide in the deposits.
[0352] (10) Electrodeposition of CO
[0353] Bath 4 (0.05M Co sulfate) and bath 5 (0.05M Co sulfate,
0.15M glycine) shown in Table 9 were used to study the effect of
glycine on the electrodeposition of Co at 25 and 60.degree. C. FIG.
31 shows the Hull cell patterns. Adding glycine (bath 5)
effectively increased CD.sub.max, especially at 60.degree. C.
CD.sub.max increased from 90 to 500 mA/cm.sup.2 at 60.degree. C. by
the addition of 0.15M glycine into bath 4. It has been reported
that the Co-glycine complex can inhibit the formation of
Co(OH).sub.2.[C. F. Diven,F. Wang, A. M. Abukhdeir, W. Salah, B. T.
Layden, C. F. Geraldes, and D. M. Freitas, Inorg. Chem., 42, 2774,
(2003)] Therefore, addition of glycine appears to prevent the
formation of Co(OH).sub.2, and extended the metallic deposit region
to higher CDs.
TABLE-US-00009 TABLE 9 The effect of glycine on electrodeposition
of Co [Sm(NH.sub.2SO.sub.3).sub.3] [Glycine] CD.sub.max EXP # Bath
(M) [CoSO.sub.4] (M) (M) pH T (.degree. C.) (mA/cm.sup.2) 151 4 0
0.05 0 5.6 25 30 152 60 90 153 5 0.15 4.5 25 110 154 60 500 *Total
charge = 100 C, applied current = 4.5 A, substrate area = 15
cm.sup.2 (10 cm .times. 1.5 cm), no agitation.
[0354] An increase in solution temperature also increased
CD.sub.max. Deposits obtained from bath 5 increased CDma, from 110
to 500 mA/cm.sup.2 by increasing solution temperature from 25 to
60.degree. C. In summary, addition of glycine and increase of
solution temperatures resulted in higher CD.sub.max.
[0355] (11) Electrodeposition of Co--Sm Alloys
[0356] As discussed in the previous sections, glycine can form
complexes individually with both Sm and Co ions. Sm.sup.3+
complexed with glycine can not be electrodeposited to Sm (FIG. 30).
Previous work [M. Schwartz, F. He, N. Myung, and K. Nobe, in
Magnetic Materials, Processes, and Devices V. Applications to
Storage and Microelectromechanical Systems (MEMS), L. T. Romankiw,
S. Krongelb, and C. H. Ahn, Editors, PV 98029, p. 646, The
Electrochemical Society Proceedings Series, Pennington, N.J.
(1999)] has shown that Co--Sm alloys can be electrodeposited from
aqueous solutions containing Sm.sup.3+, Co and glycine (or other
appropriate complexers). Electrodeposition of Co--Sm alloys have
been studied at 25 and 60.degree. C. in the absence and the
presence of glycine at two concentrations; Bath 6 (1M Sm sulfamate,
0.05M Co sulfate), bath 1 (1M Sm sulfamate, 0.05M Co sulfate, 0.15M
glycine) and bath 7 (1M Sm sulfamate, 0.05M Co sulfate, 3M glycine)
were selected, as shown in Table 10. The Hull cell patterns and Sm
content of deposits from these three baths are shown in FIG. 32
(for 25 and 60.degree. C.) and FIG. 33 (for 60.degree. C. only),
respectively. In the absence of glycine, deposits had metallic
appearance but contained considerable hydroxides/oxides.
TABLE-US-00010 TABLE 10 The effect of glycine on electrodeposition
of Co--Sm alloys at 25 and 60.degree. C. [CoSO.sub.4] [Glycine] T
CD.sub.max EXP # Bath [Sm(NH.sub.2SO.sub.3).sub.3] (M) (M) (M) pH
(.degree. C.) (mA/cm.sup.2) 15 6 1.00 0.05 0 5.8 25 20 3 1 0.15 5.7
50 25 7 3.00 4.0 40 22 6 1.00 0.05 0 5.8 60 150 6 1 0.15 5.7 750 31
7 3.00 4.0 650 *Total charge = 100 C, applied current = 4.5 A,
substrate area = 15 cm.sup.2, no agitation.
[0357] The addition of glycine extended the metallic deposit region
by increasing CD.sub.max. CD.sub.max from 0 to 3M (FIG. 32)
increased, reached a maximum, and then decreased with increased
glycine concentration. At 60.degree. C., for example, the
CD.sub.max increased from 150 mA/cm.sup.2 (no glycine), reached a
maximum of 750 mA/cm.sup.2 (0.15M glycine), then slightly decreased
to 650 mA/cm.sup.2 (3M glycine).
[0358] Differing from other metallic deposits observed in previous
sections, it was noted that the surfaces of "metallic" deposits
from bath 6 (no glycine) at 25 and 60.degree. C. were covered by a
thin gray coating. These films contained oxides and hydroxides of
Co and Sm (FIGS. 34(b) & (c)). On the other hand,
oxides/hydroxides were not found in the metallic deposit obtained
from the bath 1 (with 0.15M glycine) at 60.degree. C. (650
mA/cm.sup.2) (FIG. 34(a)) and only a weak (11.0) peak was observed
at 25.degree. C. (50 mA/cm.sup.2) (FIG. 34(b)). The addition of
glycine apparently suppressed formation of oxides and hydroxides.
In the absence of glycine, bath 6 became unstable and white
precipitates formed after 24 hours. Addition of glycine apparently
stabilized the solution preventing the formation of hydroxides in
the solution.
[0359] It is interesting that the Sm oxides included SmO in the
deposits obtained from solutions without glycine (FIGS. 34(b) &
(c)) indicating that Sm(II) may form during electrodeposition.
Reduction potential of Sm.sup.2+ to Sm is much more negative,
E.degree.=-2.67 V.sub.SHE, than Sm.sup.3+/Sm.sup.2+
(E.degree.=-1.55V.sub.SHE).W. M. Latimer, The Oxidation States of
the Elements and Their Potentials in Aqueous Solution,
Prentice-Hall, N.Y., pp. 286-295 (1952) Glycine forms complexes
with Co and Sm ions enabling co-deposition of Co--Sm alloys. By
addition of 0.15M glycine (bath 1), a relatively high Sm deposit
content of 25 at % was obtained at 650 mA/cm.sup.2 and 60.degree.
C.
[0360] By addition of excess glycine (3M glycine, 60.degree. C.
bath 7), CD.sub.max decreased (FIG. 32(f)) and Sm deposit content
decreased (FIG. 33). At 60.degree. C. and 400 mA/cm.sup.2, for
example, the Sm content drops substantially from 14.7 to 2.9 at %
as the concentration of glycine increased from 0.15 to 3M. Excess
glycine may complex virtually all of the Co.sup.2+ and additional
Sm.sup.3+ resulting in the formation of mononuclear complexes,
Co(gly).sup.-.sub.3 and Sm(gly).sup.-.sub.3, at the expense of
forming the heterodinuclear complexes required for the codeposition
of Co--Sm alloys as proposed previously.[N. V. Myung, M. Schwartz,
and K. Nobe, in Fundamental Aspects of Electrochemical Deposition
and Dissolution, M. Matlosz, D. Landolt, R. Aogaki, Y. Sato, and J.
B. Talbot, Editors, PV 99-33, p. 263, The Electrochemical Society
Proceedings Series, Pennington, N.J. (1999).]
[0361] (12) Effect of Ammonium Sulfamate Concentration
[0362] Ammonium sulfamate as supporting electrolyte in the plating
bath has been used in a previous study [M. Schwartz, F. He, N.
Myung, and K. Nobe, in Magnetic Materials, Processes, and Devices
V. Applications to Storage and Microelectromechanical Systems
(MEMS), L. T. Romankiw, S. Krongelb, and C. H. Ahn, Editors, PV
98029, p. 646, The Electrochemical Society Proceedings Series,
Pennington, N.J. (1999)]. However, the effect with/without ammonium
sulfamate on deposit properties (especially Sm content) has not
been carefully studied yet. Bath 1 (1M Sm sulfamate, 0.05M Co
sulfate, 0.15M glycine) and bath 8 (1M Sm sulfamate, 0.05M Co
sulfate, 0.15M glycine, 1M NH.sub.4 sulfamate) were used to study
the effect of ammonium sulfamate as shown in Table 11. The Hull
cell patterns of these deposits are given in FIG. 35.
TABLE-US-00011 TABLE 11 The effect of ammonium sulfamate
[Sm(NH.sub.2SO.sub.3).sub.3] [CoSO.sub.4] [Glycine]
[NH.sub.4(NH.sub.2SO.sub.3] T CD.sub.max EXP # Bath (M) (M) (M) (M)
(.degree. C.) (mA/cm.sup.2) 3 1 1.00 0.05 0.15 0 25 50 6 60 750 34
8 1 25 240 40 60 900 *Total charge = 100 C, applied current = 4.5
A, substrate area = 15 cm.sup.2 (10 cm .times. 1.5 cm), no
agitation.
[0363] The presence of 1M ammonium sulfamate resulted in increased
CD.sub.max at 25 and 60.degree. C. For example, at 25.degree. C.,
the CD.sub.max increased from 50 to 240 mA/cm.sup.2 by addition of
1M ammonium sulfamate (FIGS. 35(a) and (c)), but Sm content
decreased, especially at 60.degree. C. and higher CDs (FIG. 36). At
60.degree. C., the highest Sm deposit content dramatically dropped
from 25 to 12 at % (at 650 mA/cm.sup.2) by addition of 1M ammonium
sulfamate.
[0364] (13) Results and Discussion of Pulse Current (PC)
Electrodeposition
[0365] Effect of peak current density (PCD) and solution
temperature: Since metallic deposits obtained at higher CD have
higher Sm contents, PC electrodeposition, which enables higher PCD
than DC, was used to increase the Sm deposit content. Bath 1 was
used to study the effects of PCD and solution temperature on PC
electrodeposition. Experimental conditions are given in Table 12,
and Hull cell patterns of deposits are shown in FIG. 37.
TABLE-US-00012 TABLE 12 The Effect of Peak Current Density T.sub.on
T.sub.off Frequency PCD.sub.max.(or CD.sub.max) EXP # Bath (ms)
(ms) Duty Cycle (Hz) T (.degree. C.) (mA/cm.sup.2) 52 1 10 90 0.1
10 25 200 49 0.05 0.45 2k 1160 56 10 90 10 60 1000 53 0.05 0.45 2k
2400 3 1 DC 25 50 6 60 750 *In PC, total charge = 50 C, substrate
area = 7.5 cm.sup.2 (10 cm .times. 0.75 cm); at 25.degree. C.,
applied current = 4.5 A, at 60.degree. C., applied current = 7 A.
In DC, total charge = 100 C, substrate area = 15 cm.sup.2 (10 cm
.times. 1.5 cm), applied current = 4.5 A. Both DC and PC were no
agitation
[0366] It was observed that PC electrodeposition has a larger
maximum peak current density (PCD.sub.max) than DC (FIG. 37); for
example, at 25.degree. C., the CD.sub.max for DC was 50 mA/cm.sup.2
and the PCD.sub.max for T.sub.on=0.05 ms (duty cycle=0.1) was 1160
mA/cm.sup.2. As DC, the PCD.sub.max increased with increased
solution temperature. For instance, for deposits obtained from bath
1 at T.sub.on=0.05 ms (duty cycle=0.1), PCD.sub.max increased from
1160 to 2400 mA/cm.sup.2 by raising the solution temperature from
25 to 60.degree. C.
[0367] At 25.degree. C., because PC was able to obtain metallic
deposits at higher PCD than DC, the highest Sm deposit content
achieved by PC was greater than DC (FIG. 38). PC electrodeposition
(T.sub.on=0.05 ms, duty cycle=0.1) resulted in a maximum Sm content
of 19 at % at 580 mA/cm.sup.2 and 25.degree. C. At the same
temperature (25.degree. C.) DC electrodeposition had a maximum Sm
deposit content of 5 at % at 25 mA/cm.sup.2.
[0368] On the other hand, at higher solution temperature
(60.degree. C.) PC did not result in a higher maximum Sm deposit
content than DC electrodeposition; the maximum Sm deposit content
by PC (.gamma.=0.1, T.sub.on=0.05 ms) was 9.5 at % (1900
mA/cm.sup.2) which was less than by DC (Sm=18.5 at % at 600
mA/cm.sup.2). At 60.degree. C., although PC had higher PCD.sub.max,
the increase rate in Sm content for PCD (or CD)
SMcontent PCD ( or CD ) , ##EQU00006##
was much lower for PC than for DC leading to this result. To sum
up, at 25.degree. C., a higher maximum Sm deposit content was
obtained by PC than by DC electrodeposition; at 60.degree. C., DC
had a higher maximum Sm deposit content than PC.
[0369] Effect of T.sub.on: T.sub.on, relates to the total charge
passed per pulse cycle; the longer T.sub.on, the more charge passed
for electrochemical reactions. All the deposits were obtained from
25.degree. C. bath 1; the experimental conditions are given in
Table 13; and the Hull cell patterns of deposits are shown in FIG.
39.
TABLE-US-00013 TABLE 13 The effect of T.sub.on T.sub.off Duty
Frequency T PCD.sub.max EXP # Bath T.sub.on (ms) (ms) Cycle (Hz)
(.degree. C.) (mA/cm.sup.2) 49 1 0.05 0.45 0.1 2k 25 1100 50 0.1
0.9 1k 1100 51 1 9 100 380 52 10 90 10 200 *Total charge = 50 C,
substrate area = 7.5 cm.sup.2 (10 cm .times. 0.75 cm), no
agitation; applied peak current = 4.5 A.
[0370] At shorter T.sub.on higher PCD.sub.max were obtained (FIG.
39). Shorter T.sub.on resulted in lower Sm deposit content but
since the metallic region was significantly extended (greater
PCD.sub.max), higher Sm content could be obtained. Deposits
obtained from 25.degree. C. bath 1 for T.sub.on=0.1 ms, duty
cycle=0.1, for instance, had 22 at % Sm content at 650 mA/cm.sup.2
(FIG. 40).
[0371] (14) Effect of Duty Cycle
[0372] Bath 1 was used to study the effect of duty cycle on
electrodeposited Co--Sm alloys; experimental conditions are given
in Table 14 and FIG. 41 show their Hull cell patterns.
TABLE-US-00014 TABLE 14 The effect of duty cycle T.sub.on T.sub.off
Duty Frequency T PCD.sub.max EXP # Bath (ms) (ms) Cycle (Hz)
(.degree. C.) (mA/cm.sup.2) 112 1 0.1 1.90 0.050 500 25 1300 111
1.23 0.075 750 1250 50 0.9 0.1 1k 1100 83 0.4 0.2 2k 160 84 0.23
0.3 3k 80 3 0 1 DC 50 (continuous) *Total charge = 50 C, substrate
area = 7.5 cm.sup.2 (10 cm .times. 0.75 cm), no agitation and
applied peak current = 4.5 A.
[0373] Smaller duty cycle led to higher PCD.sub.max For example,
PCD.sub.max dramatically increased from 50 to 1300 mA/cm.sup.2 by
decreasing duty cycle from 1 to 0.05 (FIG. 41); Sm deposit content
decreased (FIG. 42). For deposits obtained at 600 mA/cm.sup.2, Sm
deposit content decreased from 21 to 7.5 at % by decreasing the
duty cycle from 0.1 to 0.05.
[0374] 3. Parametric Aqueous Electrodeposition Studies of Co--Sm
Alloys
[0375] Iron group (IG)-rare earth (RE) alloys are known for their
ferromagnetic and energy storage applications and resistance to
aggressive environments. Co--Sm alloys, such SmCo.sub.5 and
Sm.sub.2Co.sub.17, have already been commercialized for their high
performance magnetic properties. These films have been prepared by
sputtering [H. C. Theuerer, E. A. Nesbitt and D. D. Bacon, J. Appl.
Phys., 40, 2994 (1969).], evaporation [V. Geiss, E. Kneller and A.
Nest, Appl. Phys., A27, 79 (1982).], and plasma spraying [K. Kumar,
D. Das and E. Wettstein, J. Appl. Phys., 49, 2052 (1978).].
[0376] SmCo.sub.5 alloys have very large coercivities as a result
of its considerable magnetic anisotropy constant (ku) of about
10.sup.7J/m.sup.3, and they also have high Curie temperatures. The
latter enables high operating temperatures for permanent magnet
applications as in magnetic coupling, sensors, nano and micro
systems, servo motors, etc. Although CoSm alloys are expensive,
their superior high temperature magnetic performance and
reliability outweigh the costs for military and
aeronautical/aerospace applications [M. Rassignol and J. P. Yonnet,
Magnetism, II-Materials and Applications, E. T. de Lacheisserie, D.
Gignoux and M. Schlenker, Eds., Chap. 15, Kluwer Academic
Publishers, The Netherlands (2002).]. The development of an aqueous
electrodeposition process for Co--Sm alloys will substantially
lower manufacturing costs.
[0377] The high perpendicular coercivities of Co--Sm alloys make
them eminently suitable for ultra high density information storage
as in hard disk drives [M. H. Kryder, Applied Magntism, R. Gerber,
C. D. Wright and G. Asti, Eds., p. 39, Kluwer Academic Publishers,
The Netherlands (1994); R. C. O'Handley, Modern Magnetic Materials,
Chaps. 13 & 17, John Wiley & Sons Inc., New York (2000); J.
Sayama, K. Mizutani, T. Asahi, J. Ariake, K. Ouchi, S. Matsumura
and T. Osaka, J. Magn. Magn. Mater., 287, 239 (2005).]. Iwasaki and
Nakamura had earlier proposed (1977) perpendicular magnetic
recording [S. Iwasaki and Y. Nakamura, EEE Trans. Mag., MAG-13,
1272 (1977).], and it has now been commercially realized.
[0378] Like other rare earth metals, electrodeposition of metallic
samarium from aqueous electrolytes has not been achieved.
Similarly, refractory metals such as W, Mo and V also have not been
electrodeposited from aqueous media. However, electrodeposition of
these metals from nonaqueous media can be done [N. Usuzaka, H.
Yamaguchi and T. Watanabe, Mater. Sci. Eng., A99, 105 (1988).].
Although pure metals of W, Mo and V have not been electrodeposited
from aqueous media, electrodeposition of alloys of W and Mo with
the iron group metals (Ni, Fe, Co) have been readily done for over
60 years [M. L. Holt and M. L. Nielsen, Trans. Electrochem. Soc.,
82, 193 (1942); H. J. Seim and M. L. Holt, Ibid, 96, 205 (1949).],
IG-V binary and ternary magnetic thin film alloys by
electrodeposition from aqueous solutions have been reported
recently [C. Arcos, M. Schwartz and K. Nobe, Plat. Surf Finish., 90
(6), 46 (2003).].
[0379] More recently, IG-RE alloy electrodeposition from aqueous
media has been achieved by our group by the use of glycine and
other aminocarboxylates as complexers [L. Chen, M. Schwartz and K.
Nobe, Proc. Electrochem. Soc., PV96-19, 239 (1996); M. Schwartz, F.
He, N. Myung and K. Nobe, Ibid., PV98-20, 646 (1999); N. Myung, M.
Schwartz and K. Nobe, Ibid., PV99-33, 263 (1999); M. Schwartz, N.
Myung and K. Nobe, J. Electrochem. Soc., 151 (7), C468 (2004). 17.
H. S. Cho, IEEE Trans. Magn., 33 (5), 2890 (1 997).]. The metal
ions and glycine are known to faun hetero-nuclear glycinato
coordinated complexes in aqueous solutions.
[0380] a. Experimental
[0381] Unless otherwise noted, the plating solutions consisted of
1M samarium sulfamate, 0.05M cobalt sulfate, 0.15M glycine as the
complexer and 1M ammonium sulfamate as the conducting salt; also
the total charge passed was 50 coulombs. The pH value of the
plating bath was 5.2 as measured at 25.degree. C. Various current
densities and bath temperatures (25-60.degree. C.) were used to
obtain deposits; solutions were not agitated during
electrodeposition.
[0382] An EG&G PAR potentiostat, model 173, served as the power
source for electrodeposition. Brass panels (2.times.1.9 cm) served
as cathodes and a platinum sheet (3.times.6 cm) was used as the
anode. The brass panels were mechanically cleaned, soaked in
alkaline solution for 10 min., rinsed in deionized water and
immersed in 10% HCl for 30 seconds.
[0383] The ratios of the samarium and cobalt deposit content was
determined by energy dispersive x-ray analysis (EDX); deposit
content of cobalt was also determined by atomic absorption
spectrophotometry (AA). The microstructure, crystal orientation and
grain size were determined by x-ray diffraction (XRD) and surface
morphology by scanning electron microscopy (SEM). Magnetic
properties were determined by a vibrating sample magnetometer
(VSM), model 1660 ADE Tech.).
[0384] b. Results and Discussions
[0385] The experimental data presented in the figures are for
deposits which had metallic appearance. In each case, at higher
current densities (CD), deposits were non-metallic and these
results are not shown.
[0386] FIG. 43 shows the effect of increased solution temperature
on the applied CD range. At 25.degree. C., the effective CD for
metallic deposits was limited to 350 mA/cm.sup.2, whereas for a
solution temperature of 60.degree. C., the CD could be increased to
700 mA/cm.sup.2, resulting in increasing deposit Sm content from 8
to 17 at %. Although the (linear) deposition rate was greater at
25.degree. C., extrapolation indicated that at 450 mA/cm.sup.2 the
deposition rate at 60.degree. C. would have exceeded that of the
rate at 25.degree. C. Elevated solution temperatures permit higher
CDs depositing metallic appearing deposits with deposit Sm content
reaching 17.2 at % at CD.about.700 mA/cm.sup.2 and a temperature of
60.degree. C. The current efficiencies (CE) drop sharply between 50
mA/cm.sup.2 (20%) and 200 mA/cm.sup.2 (6%) with little change
between 200 mA/cm.sup.2 and 350 mA/cm.sup.2 in the 25.degree. C.
solution, whereas the CE decreases almost linearly in the
60.degree. C. solution with an apparent slope of about 1%/100
mA/cm.sup.2 (FIG. 44).
[0387] With increasing solution temperature from 25-60.degree. C.,
the deposit Sm content decreases almost linearly for CDs of 100
mA/cm.sup.2 and 300 mA/cm.sup.2, the latter being consistently 4%
higher (FIG. 45). However, the CEs were higher for the lower
applied CD (FIG. 46).
[0388] Additional parametric studies were performed to assess the
effects of agitation, the solution concentration of Sm sulfamate
and glycine, and the presence of NH.sub.4 sulfamate on the deposit
Sm content. Agitation had a greater effect on the deposit Sm
content at higher CDs while it generally increased with decrease in
solution concentration of the Sm salt from 1M. An increase in the
glycine concentration from 0.15M decreased the deposit Sm content.
Addition of the conducting salt (NH.sub.4 sulfamate) decreased the
deposit Sm content.
[0389] Magnetic saturation (Ms) values of the electrodeposits are
quite close but slightly lower than those of sputtered Co--Sm thin
films at equivalent Sm contents (FIG. 47). This is indicative of
the metallic nature of the electrodeposited Co--Sm alloys. The
electrodeposition results in this figure were obtained from
solutions with no conducting salt (NH.sub.4sulfamate). The closed
circle points represent electrodeposits obtained at 60.degree. C.
with 50 coulombs of charge passed. The open points represent
thicker deposits (500 coul. charge passed). Higher Sm content could
be obtained for thicker deposits from solutions in the absence of
NH.sub.4sulfamate (.about.33 at. % Sm, open diamonds) than in its
presence (23 at. %Sm, closed circles). Pulse current
electrodeposition (open triangles) produced metallic deposits (20
at. %Sm) for a duty cycle (7) of 0.1. Magnetic saturation of
non-metallic deposits were substantially lower than metallic
deposits of the equivalent Sm content. For example, for 17 at %Sm,
Ms of the metallic deposit was 4 times higher than the non-metallic
deposit. FIG. 48 shows that the deposit coercivities (Hc) in the
parallel direction increase only slightly with increase in deposit
Sm content, i.e., with increased CD, and is not affected by
solution temperature. However, deposit coercivities decrease
sharply in the perpendicular direction with increasing CD in
deposits from 25.degree. C. solutions, but a linear decrease with a
negative slope from 60.degree. C. solutions. Perpendicular
coercivities are significantly higher than in the parallel
direction. Thus, heat treatment of Co--Sm deposits leads to
substantially higher coercivities.
[0390] The deposit topography is affected by the applied CD and
probably also solution temperature. There is increased surface
roughness as a result of increased CD. FIGS. 49a,b show that the
absence of the conducting salt (NH.sub.4sulfamate) dramatically
results in a much smoother surface than in its presence. X-ray
diffraction spectra (XRD) (FIG. 50) indicate the 2.1 at. % Sm
deposit (100 mA/cm.sup.2) appears amorphous and the 10.4 at. % Sm
deposit (500 mA/cm.sup.2) exhibits crystalline structures with
(200) phase of Sm.sub.2Co.sub.17 alloy composition. In the absence
of NH.sub.4 sulfamate in the bath, the (201) phase of the
SmCo.sub.5 alloy as well as the Sm.sub.2Co.sub.17 (200) phase
appear in the deposits.
[0391] c. Conculsions
[0392] Sm content of metallic deposits of Co--Sm can be increased
at higher CDs from higher temperature solutions. Furthermore,
significantly higher deposit Sm content can be obtained from
solutions in the absence than in the presence of the conducting
salt (NH.sub.4 sulfamate). Co--Sm deposits with 33 at % Sm have
been obtained at 500 mA/cm.sup.2 and a solution temperature of
60.degree. C. Magnetic saturation of electrodeposits were close to
those of sputtered deposits. Perpendicular coercivities were
substantially higher than parallel coercivities for Co--Sm
electrodeposits. Heat treatment of deposits should result in an
order of magnitude increase in perpendicular coercivities.
[0393] 4. Coordination Chemistry in the Electrodeposition of IG-V,
W and Mo Alloys from Aqueous Carboxylate Solutions
[0394] Polycarboxylates, hydroxycarboxylates and aminocarboxylates
are well known additives functioning as complexing agents for the
electrodeposition of single metals and alloys from aqueous plating
baths. Tartrates and citrates are extensively employed in
electrodeposition of alloys, including the deposition of alloys
containing elements such as the refractory metals: W, Mo, V.
Although these individual metals cannot be electrodeposited from
aqueous media, alloys with the iron group metals (IG) have been
electrodeposited from aqueous solutions [A. Brenner,
Electrodeposition of Alloys, Vol. II,. Acad. Press (1963).
[0395] Brenner et al. and Holt and his co-workers have studied the
electrodeposition of IG-W and --Mo alloys from aqueous solutions
[A. Brenner, P. Burkheard and E. Seegmiller, J. Iles. NBS, 94, 351
(1947); L. E. Vaaler and M. L. Holt, Trans. Electrochem. Soc. 90,
43 (1946); L. E. Vaaler and M. L. Holt, Ibid., 94, 50 (1948); W. E.
Clark and M. L. Holt, Ibid., 94, 244 (1948); M. H. Lietzke and M.
L. Holt, Ibid., 94, 252 (1948); R. F. McElwee and M. L. Holt. I
Electrochem. Soc., 99 (2), 48 (1952).]. More recent work on the
electrodeposition of IG-X alloys has been reported for
electroplating baths containing citrates as complexers, with some
consideration given to the nature and structure of the
organometallic complexes involved [M. Schwartz, C. Arcos and K.
Nobe, Plat. Surf. Fin., 90 (6) 46 (2003); E. J. Podlaha and D.
Landolt, J. Electrochem. Soc., 143, 885 (1996); Ibid., 143 (11) 893
(1996); Ibid., 144 (5) 1672 (1997); O. Younes and E. Gileadi,
Ibid., 149, C100 (2002); O. Younes-Metzler, L. Zhu and E. Gileadi,
Electrochim. Acta, 48, 2551 (2003).]. There has been a growing
interest in determining the structures of these refractory
metal-hydroxycarboxylato--complexes by spectroscopic experiments
for biological, physiological applications [M. Tsaramyrsi, M. K.
aliva, A. Salifoglou, C. P. Raptopoulou, A. Terzis, V. Tangoulis
and J. Giapintzakis, Inorg. Chem., 40 (23), 5773 (2001); T. Kiss,
P. Buglyo'. D. Sanna, G. Micera, P. Decock and D. Dewaele, Inorg.
Chem. Acta, 239, 145 (1995); 9. Z-H Thou, H-L Wan and K-R Tsai, 1
Chem. Soc., Dalton Trans., 4289 (1999). Z-H Thou, H-L Wan and K-R
Tsai, Inorg. Chem., 39, 59 (2000); Z-H Thou, S-Y Hou and H-L Wan,
J. Chem. Soc., Dalton Trans., 1393 (2004).].
[0396] Since the early 1990s, this laboratory has been
investigating the electrodeposition of IG-V alloys in order to
improve the physical properties as well as the corrosion resistance
of the high magnetic moment 90Co10Fe alloys, as suggested by Liao
[S. H. Liao, IEEE Tran. Magn 23, 2981 (1987).]. In addition, the
electrodeposition of V-Petinendur (49Co49Fe2V) was investigated
because of its excellent magnetic properties; it has not had wide
commercial applications because of its high manufacturing costs,
however [G. Y. Chin and J. H. Wernick in Ferromagnetic Materials,
vol. 2, p. 168, E. P. Wohlfarth, Ed., North-Holland, Amsterdam,
(1980).]. Development of a commercial electrodeposition process
would sharply reduce these costs and greatly expand applications in
miniaturized electronic devices.
[0397] Some of our interest in the electrodeposition of the IG-X
alloys (X=V. W and Mo) dates to the early work (1948) of one of us
(M. S.) who developed a commercial Co--W plating process using an
ammoniacal citrate bath. He found that when the Co and
WO.sub.4.sup.2- salt solutions are mixed, a cobalt tungstate
precipitate forms which dissolves with the addition of citrate. His
experimental results lead him to conjecture that both Co(II) and
W(VI) are coordinated in the same complex with deprotonation of the
carboxylate forming a heteronuclear biscitrato--complex.
Subsequently, later work by Zhuravleva and co-workers on the
complexation of oxyvanadium and IG ions with citric acid indicated
the existence of homo-dinuclearVO-biscitrato- and hetero-dinuclear
IGbiscitrato- complexes [Y. I. Sal'nikov, F. V. Devyatov, N. E.
Zhuravleva, D. V. Golodnitskaya, Jh. Neorgan Khimi., 29, 2273
(1984); A. N. Glebov, Y. I. Sal'nikov, N. E. Zhuravleva, V. V.
Chevela and P. A. Vasil'ev, Ibid., 27, 2146 (1982); N. E.
Zhuravleva and Y. I. Sal'nikov, Proc. Tech. Inst. Chem. and Chem
Tech., 32 (2) 25 (1989).].
[0398] Plating baths are presented in Table 15, Table 16, Table 17,
and Table 18. NH.sub.3 (aq) and HCl (or sulfamic acid) were used to
adjust solution pH. Plating baths were maintained at room
temperature and were quiescent or mechanically stirred, as
required. DC was provided by a PAR potentiostat or a Kraft
Dynatronix power supply (Model DPR 20-5-10). Total charge passed
was controlled to produce desired film thicknesses.
[0399] Brass panels served as cathodes and the anode was a cobalt
(or Pt) sheet. The brass panels were scrubbed with Alconox, rinsed
in deionized water and then activated in concentrated HCl. The
deposits were dissolved in concentrated HNO.sub.3 for analysis.
Cobalt and vanadium deposit contents were determined by atomic
absorption spectrophotometry (AA). Cobalt was also determined by
energy dispersive spectroscopy (EDX). Tungsten and molybdenum were
analyzed by gravimetric methods as well as EDX. Scanning electron
microscopy (SEM) and x-ray diffraction were used to characterize
the deposits. Magnetic properties of the electrodeposits were
obtained with vibrating sample magnetometer (VSM) (ADETech, Model
1660).
[0400] a. IG-Rare Earth (SM) Coordination Compounds
[0401] Initial investigation of the electrodeposition of IG-RE
alloys was reported in 1996 [L. Chen, M. Schwartz and K. Nobe, in
Electrodeposited Thin Films. M. Paunovic and D. A. Scherson,
Editors, PV96-19, p. 239, The Electrochem. Soc. Proceedings Series,
Pennington, N.J. (1996).]. Hydroxycarboxylate and other carboxylate
salts as complexers appeared to be inferior to glycine and other
amino acid salts. The bipolarity, i.e. zwitterionic properties, of
glycine (and other aminoacids) results in ionic complexes at the
cathode surface as the pH fluctuates. As a result, structures and
deposition mechanisms of IG-RE dinuclear diglycinato- and
triglycinato-coordination complexes have been considered as the
vehicles for the co-deposition of the IG-RE alloys [M. Schwartz, M.
V. Myung and K. Nobe, J. Electrochem. Soc., 151. C468 (2004).].
Continued development indicates the deposit Sm contents and
resulting magnetic properties could be varied, depending on the
solution composition, CD and temperature [J. C. Wei, M. Schwartz
and K. Nobe, Trans. Electrochem. Soc. (in press).]. Table 15
summarizes typical solution composition ranges and with the
deposition conditions selected, result in wide variations in
deposit Sm content. The glycine: Co ratio in these solutions was
3:1 with Sm.sup.3+ concentration in excess. Solutions with lower Co
and Sm concentrations resulted in higher deposit Sm contents (15-18
a/o) than more concentrated solutions. In the latter solution, FIG.
51 shows the deposit Sm content increased linearly with increasing
CD while the CE decreased sharply as CD increased to .about.100
mA/cm.sup.2, reaching a plateau with increased CD, indicating a
possible relation of hydrogen evolution to deposit content.
TABLE-US-00015 TABLE 15 Representative plating baths for Co--Sm
alloys Co.sup.2+ (as sulfamate) 0.06M-0.12M Sm.sup.3+ (as
sulfamate) 0.3M-0.9M Glycine 0.18M-0.36M NH.sub.4(NH.sub.2SO.sub.3)
1.0M NH.sub.4OH pH 6.5-7.0
TABLE-US-00016 TABLE 16 Representative plating baths for IG-V
alloys Binary Ternary Co.sup.2+ 0.3M 0.15-0.3 M VO.sup.2+ 0.15-0.3
0.15-0.17 M Fe.sup.2+ 0.03M-0.15M (Ni.sup.2+) (0.05M)
Na.sub.3C.sub.6H.sub.5O.sub.7 0.25-0.35 M 0.25 M H.sub.3BO.sub.3
0.1 M NH.sub.4Cl 1.0 M NH.sub.4OH pH 6.0-7.5
[0402] b. IG-Vanadium Coordination Compounds
[0403] Electrodeposition of binary and ternary IG-V alloys from
citrate solutions has been reported [M. Schwartz, C. Arcos and K.
Nobe, Plat. Surf. Fin., 90 (6) 46 (2003); B. Y. Yoo, dissertation,
UCLA, 2003; also unpublished data, UCLA. 2004.]. Although
"representative" solution compositions are given in Table 16, wide
variations in concentrations provide flexibility in the resulting
deposit compositions and their magnetic properties. In binary alloy
deposits, the V contents decreased: Co>Fe>Ni and the magnetic
properties varied with the deposit V content; magnetic saturation
decreased and coercivities increased with increasing deposit V
content (Table 19). Thus, the ability to control deposit
composition and their magnetic properties provides "tailor-made"
deposits for various electronic applications. FIG. 52 indicates the
wide variations in Co--V electrodeposits vs CD with deposit Co
content increasing with increasing CD, whereas Fe-V electrodeposits
exhibit very little change in deposit compositions vs CD, with
deposit V contents <2 w/o over the CD range, 5-50 mA/cm.sup.2
[B. Y. Yoo, dissertation, UCLA, 2003; also unpublished data, UCLA.
2004.]. Magnetic saturation, B.sub.s, of ternary CoFeV
electrodeposits exceeded that of the binary CoV and FeV
electrodeposits. Ternary 48Co49.8Fe2.2V electrodeposits
approximating bulk 2V-Permendur (48Co48Fe2V) exhibited a magnetic
saturation B.sub.s of 2.32 T. Liao indicated a 90Co 10Fe
electrodeposit had a magnetic saturation of 1.9 T, exceeding that
of Permalloy (80Ni20Fe), B.sub.s=1.0 T; however, corrosion
resistance of the alloy was inferior [S. H. Liao, IEEE Tran. Magn
23, 2981 (1987).]. As shown in Table 19, addition of V to the
binary electrodeposit (87.3Co8.6Fe4.1V) improved corrosion
resistance and increased magnetic saturation, B.sub.s=2.20 T [B. Y.
Yoo, dissertation, UCLA, 2003; also unpublished data, UCLA.
2004.].
TABLE-US-00017 TABLE 17 Representative plating baths for Co--W
alloys Brenner Holt (3) (2) Brenner (2) MS (12) Gileadi (6)
[Co.sup.2+] (M) 0.213 0.6 0.42 0.12 *(Ni) [WO.sub.4.sup.2+] (M)
0.213 0.3 0.13 0.12 * [Cit.sup.3-] (M) 0.314 1.2 -- 0.48 *
[Tart.sup.2-] (M) -- -- 1.42 -- -- NH.sub.4Cl -- 0.5 0.94 0.5 *
NH.sub.4OH 7-8.5 8.5 8.5 8.5-9 8 (pH) % W, a/o >17.5 7.7 7.7-9.6
7.9-17.5 12-15 % W, w/o >40 ~20 20-50 20-40 30-35 T (.degree.
C.) 70 .gtoreq.40 .gtoreq.90 65-80 25
TABLE-US-00018 TABLE 18 Representative plating baths for IG-Mo
alloys Holt (22) Landolt (5) IG [Fe.sup.3+], [Co.sup.2+],
[Ni.sup.2+] (M) 0.3 0.2 (Ni) Na.sub.2MoO.sub.4 (M) 0.02-0.075
0.005-0.05 Na.sub.3C.sub.6H.sub.5O.sub.7 0.3 0.25-0.95 NH.sub.4OH
(pH) 10.5 9.7-10.2 T (.degree. C.) 25 25-40
TABLE-US-00019 TABLE 19 Magnetic properties of selected
electrodeposited IG-V, W, Mo alloys Co Bs (wt %) Fe (wt %) V (wt %)
W (wt %) Hc (Oe) (T) Reference 91 9 118 1.43 (20) 97.8 2.2 25 1.93
(20) 67 33 57 1.28 (19) 87.3 8.6 4.1 58 2.20 (20) 48.0 49.8 2.2 46
2.32 (20)
[0404] Nikolova and Nikolov suggested mononuclear and dinuclear
oxyvanadium citrato complexes. Based on indirect evidence,
potentiometric experiments and IR spectra, they indicated the
protonated hydroxo-group may be involved in 1:1 mononuclear
citratocomplex (stability constant=6.6.times.10.sup.8) and a
dinuclear citrato- complex with the hydroxy group or carboxylato
group bridging the two VO's (stability
constant=3.2.times.10.sup.11) [B. M. Nikolova and G. St.
Nikolov,./.Inorg. Nucl. Chem., 29, 1013 (1967).].
[0405] Zhuravleva and co-workers studied dinuclear IG
biscitrato-complexes and heteronuclear
IG-(VO).sub.2-biscitrato-complexes [Y. I. Sal'nikov, F. V.
Devyatov, N. E. Zhuravleva, D. V. Golodnitskaya, Jh. Neorgan
Khimi., 29, 2273 (1984); A. N. Glebov, Y. I. Sal'nikov, N. E.
Zhuravleva, V. V. Chevela and P. A. Vasil'ev, Ibid., 27, 2146
(1982); N.E. Zhuravleva and Y. I. Sal'nikov, Proc. Tech. Inst.
Chem. and Chem Tech., 32 (2) 25 (1989).]. Salni'kov et al.
investigated mononuclear, dihomonuclear and heteronuclear
biscitrato-complexes of Ni and Co, the latter being partially
deprotonated or completely deprotonated [Y. I. Sal'nikov, F. V.
Devyatov, N. E. Zhuravleva, D. V. Golodnitskaya, Jh. Neorgan
Khimi., 29, 2273 (1984).]. Glebov et al. indicated dinuclear
(VO).sub.2 complexes only with hydroxocarboxylic acid, e.g.,
citric, tartaric and malic acids [A. N. Glebov, Y. I. Sal'nikov, N.
E. Zhuravleva, V. V. Chevela and P. A. Vasil'ev, Ibid., 27, 2146
(1982).]. The depicted dinuclear biscitrato-coordination compound
indicates protonated hydroxy group oxygens bridging the two V
atoms. Zhuravleva and Salni'kov obtained a heteronuclear biscitrato
complex by reacting individual Cu citrate and VO citrate solutions
[N. E. Zhuravleva and Y. I. Sal'nikov, Proc. Tech. Inst. Chem. and
Chem Tech., 32 (2) 25 (1989).].
[0406] c. IG-W Coordination Compounds
[0407] Holt and his students investigated the electrodeposition of
IG-W alloys from ammoniacal citrate solutions [L. E. Vaaler and M.
L. Holt, Trans. Electrochem. Soc. 90, 43 (1946); L. E. Vaaler and
M. L. Holt, Ibid., 94, 50 (1948); W. E. Clark and M. L. Holt,
Ibid., 94, 244 (1948); M. H. Lietzke and M. L. Holt, Ibid., 94, 252
(1948); R. F. McElwee and M. L. Holt. I Electrochem. Soc., 99 (2),
48 (1952).]. After complexation, atomic hydrogen reduction has been
suggested to explain the co-deposition of IG-W alloys by proposing
a two-step reduction hypothesis involving alternating deposition of
the IG species which catalyzed the reduction of the tungstate ion
and resulted in a laminar deposit, based on polarographic studies
and cathode potential measurements, the latter being lower in
solutions containing tungstate ions.
[0408] Younes and Gileadi concluded a heteronuclear Ni-W
monocitrato complex with the carboxylate triply deprotonated is the
precursor for the electrodeposition of the Ni--W alloy [O. Younes
and E. Gileadi, Ibid., 149, C100 (2002); O. Younes-Metzler, L. Zhu
and E. Gileadi, Electrochim. Acta, 48, 2551 (2003).]. The complex
is the result of the reaction of individual Ni and W citrate
complexes. A similar reaction with a Ni-biscitrato-complex was
considered unlikely because both reacting complexes would be highly
charged. They also reported that elimination of NH.sub.4 salts and
NH.sub.3 (aq.) from similar solutions resulted in amorphous
deposits with increased deposit W contents, but substantial CE
reduction.
[0409] Brenner et al. indicated an inorganic Co--W solution (no
citrate) resulted in deposits containing 20-27 wt.% W at CDs 20-50
mA/cm.sup.2, respectively [A. Brenner, P. Burkheard and E.
Seegmiller, J. Iles. NBS, 94, 351 (1947).]. Without the presence of
NH.sub.4 salts, the solubility of Co and W is reduced and the CE is
quite low, making the solution unsuitable for practical
applications. In the tartrate complexed Co--W solution (Table 17),
the presence of alkali cations (Na, K tartrate) resulted in
diminished deposit W contents as compared to ammonium tartrate
solutions, another indication of the positive effect of the
presence of NH.sub.4 ions.
[0410] d. IG-Molybdenum Coordination Compounds.
[0411] Holt and students extended their studies of the
electrodeposition of IG-W alloys to IG-Mo alloys from equivalent
solution compositions, as shown in (Table 18), [J. Seim and M. L.
Holt, Trans. Electrochem. Soc., 95, 205 (1949); D. W. Ernst, R. F.
Amlie and M. L. Holt, J. Electrochem. Soc., 102 (8), 461 (1955); D.
W. Ernst and M. L. Holt, Ibid., 105 (11), 686 (1958).]. Initially,
Hull Cells were utilized to determine pH, temperature and CD ranges
for bright, metallic deposits and resulting deposit composition and
CEs. Various ligands were classified as "good" or "poor": For
Ni--Mo, citrate and tartrate were considered "good"; for Co--Mo,
the "good" ligands were extended to include malate (and malic acid)
and glycolic acid. Sodium citrate was considered superior to citric
acid or ammonium citrate.
[0412] Similar to IG-W electrodeposition, deposit Mo contents
varied with the co-deposited IG metal: Fe (59%)>Co (40%)>Ni
(20%). The CEs were inversely related to the deposit Mo contents:
Ni (75-85%)>Co (50-60%)>Fe (10-20%), which seems to indicate
a role for adsorbed hydrogen atoms in the deposition process.
[0413] Podlaha and Landolt studied the effect of varying the
solution Ni:Mo ratios on mass transport and kinetically controlled
processes with rotating cylindrical electrodes [E. J. Podlaha and
D. Landolt, J. Electrochem. Soc., 143, 885 (1996); Ibid., 143 (11)
893 (1996); Ibid., 144 (5) 1672 (1997).]. In addition to the metal
salts, the ammoniacal solution contained sodium citrate; no
conducting salts were added (Table 18). The concentration of
NH.sub.3 (aq.) appears to be critical with respect to the deposit
Mo content. "High" NH.sub.3 (aq.) concentrations resulted in high
CEs 90% and lower deposit Mo content; most of the data presented
were obtained with 0.28 M NH.sub.3 (aq.). A deposition mechanism
whereby Mo is deposited from an intermediate (Ni--Mo) complex
either adsorbed or dissolved in the solution is proposed with Ni
depositing independently and considered the catalyst for the
electrodeposition of the alloy. The model is extended to include
codeposition of Co--Mo and Fe--Mo and explain the differing effects
of the IG species on the deposit Mo content by including the
additional presence of a single IG complex with a two-step
reduction.
[0414] Zhou and collaborators prepared and determined the
structures of various Mo, W, and V citrato-coordination compounds,
which are precursors to FeMo cofactors in nitrogenase protein
catalysts, using IR and NMR spectroscopies and Xray diffraction [9.
Z-H Thou, H-L Wan and K-R Tsai, 1 Chem. Soc., Dalton Trans., 4289
(1999). Z-H Thou, H-L Wan and K-R Tsai, Inorg. Chem., 39, 59
(2000); Z-H Thou, S-Y Hou and H-L Wan, J. Chem. Soc., Dalton
Trans., 1393 (2004).]. Tridentate Binuclear biscitrato-complexes
convert to bidentate mononuclear biscitrato ions with excess citric
acid (pH 3.5). Each ligand is coordinated as a bidentate ligand
through the deprotonated central carboxylato- and vicinal
hydroxy-groups with the terminal carboxylate groups uncomplexed.
The structure of the tridentate citratocomplexes depends on the
degree of protonation of the reacting ligand and solution pH.
Mononuclear monocitrato-complex converts to dinuclear
biscitrato-complex with the two metal atoms connected via an oxygen
bridge and two oxygen atoms covalently bonded to each metal atom in
lower pH solution with valencies depending on whether or not the
terminal carboxylate groups are protonated.
[0415] e. Structure of IG-RE-Glycine Complexes
[0416] The zwitterionic structure of glycine (gly) protonates or
deprotonates depending on the solution pH, as shown FIG. 53a.
Glycine usually coordinates through the carboxylate groups forming
O-M-O bonds; it can also form O-M-N and N-M-N bonds [C. P. Sinha,
Complexes of the Rare Earths, Pergamon Press, 1966.]. Single metal
(i.e., IG.sup.2) complexes are probably mononuclear monoglycine
bidentate chelate complexes. For homo- or hetero-dinuclear
complexation, multiligand complexes are required through N-MI-N and
O-M.sub.2-O bonds. Both IG and RE cations are likely in a
hetero-dinuclear trisglycine complex as in FIG. 53b. However,
because of the bipolar character of glycine, it can simulate
polymerization by electrostatic attraction between deprotonated
zwitterions, mimicing dip eptide or trip eptide structures through
O--N "bonds". In the case of the heteronuclear IG-RE complex,
quasi-digly (FIG. 53c) or trigly (FIG. 53d) complexes can be formed
and adsorbed at the cathode surface as the cathode film pH
fluctuates.
[0417] f. Structure of IG-VO-Biscitrate Complexes
[0418] Citric acid can form di-, tri- or tetra-dentate complexes
with metal ions, depending on the degree of deprotonation. The
structure of the binary IG-VO citrate complex (FIG. 54a) has one
carboxylate group protonated with the hydroxy-hydrogen of each
citrate ligand attracted to the VO, possibly forming H-bonds. The
depicted complex structure shows partial deprotonation of the
citrate moiety, resulting in a zero-valent complex. With continued
deprotonation, the complex becomes anionic with increasing negative
charges. Thus, the degree of protonation/deprotonation of the
carboxylatogroups is dependent on solution pH. As the pH in the
cathode film fluctuates slightly, the forms of the coordination
complex may equilibrate. FIG. 55 a indicates the hydroxy hydrogen
from each citrate ligand reacts with the oxyvanadium (VO) component
in step 2, leaving the IG-V citrate complex [IG.sup.IIV.sup.IV
(C.sub.6H.sub.SO.sub.7).sub.2].sup.0 to be step-wise reduced by
hydrogen atoms to deposit the IG-V alloy.
[0419] FIG. 54b shows the structure of the ternary IG-IG-V-citrate
complex. After removal of the oxygen in the oxyvanadium (VO)
component, as the binary complex, a similar sequential reduction
process occurs to electrodeposit the ternary alloy (FIG. 55b).
[0420] g. Structure of IG-W (Mo) Biscitrate Complexes
[0421] The tungstate (molybdate) ion reacts with citric acid and
the Id' ion to form the IG-W(Mo) citrate complex (FIG. 56). Similar
hydroxy-H bonds and reacts with one ofthe (M.sup.vI00) oxygens
converting to the complex [IG.sup.IIM.sup.VI
O(C.sub.6H.sub.SO.sub.7).sub.2].sup.0. FIG. 57, as FIG. 55, shows
the similar reduction of the IG.sup.II and M.sup.VI in the IG-M
citrate complex to the IG-M alloy.
[0422] h. Co--W/CR Composite Coating
[0423] Although there is much interest today on product
miniaturization, such as thin film magnetic devices, utilizing
these electrodeposited IG-refractory metal alloys from complexed
solutions, and the structures of V, W and Mo (poly)homonuclear and
(poly)heteronuclear polycitrato-complexes for physiological
processes, as discussed above, we also point out potential
industrial applications for thicker electroplated alloys, based on
physical, mechanical and high temperature properties such as
corrosion and wear resistance and the ability to undergo hardening
with thermal treatment. FIG. 58 illustrates the potential of
producing unique composite electrodeposits for specific
applications. In this example, corrosion resistance, wear
resistance and high temperature properties were required [M.
Schwartz in Handbook of Deposition Technologies for Films and
Coatings, R. F. Bunshah, Ed., Chpt 10, Noyes Publ. (1994).]. The
composite consists of a 80Co-20W deposit (56 .mu.m) from the
solution in Table 17 +Cr from CrO.sub.3/H.sub.2SO.sub.4 solution
(30 .mu.m)+Co--W (20 .mu.m)+Cr (thin deposit to protect deposit
edges). The specimens were subjected to high temperature
environment in air (to determine oxidation resistance) and a
carburizing atmosphere, attempting to diffuse C into the Co--W
deposit to form and disperse carbide in the deposit. To obtain good
adhesion of these layers, a thin cobalt strike (S) was deposited on
the steel substrate and between each deposit to improve deposit
adhesion.
[0424] 5. Direct Current (DC) Electrodeposition Studies
[0425] DC electrodeposition using a parallel electrode system was
investigated to determine, more precisely, the optimum operating
and aqueous bath conditions, estimated by the Hull cell studies, to
obtain high Sm content, metallic Co--Sm alloys. The purpose is to
obtain stoichiometric compositions of Co--Sm alloys to form
intermetallic Sm.sub.2Co.sub.17 (10.5 at %Sm) and SmCo.sub.5 (16.7
at %Sm), and, in addition, Sm.sub.2O.sub.7 (22.2 at %Sm) and
SmCo.sub.3 (25 at %Sm) after appropriate heat treatment
procedures.
[0426] DC electrodeposition of Co--Sm alloys from aqueous solutions
has been studied at various operating conditions (e.g., current
densities, temperatures, fluid dynamics and pHs) and plating baths
(concentration of Sm sulfamate, glycine, Co sulfate, NH.sub.4
sulfamate supporting electrolyte). Morphologies, crystalline
structures, preferred orientation and microstructures of deposits
from different electrodeposition parameters were studied and
correlated to their magnetic properties.
[0427] Samarium deposit content increased with increasing current
density. Increased solution temperatures from 25 to 60.degree. C.
effectively extended the CD to obtain metallic deposits
(CD).sub.max from 50 to 500 A/cm.sup.2 leading to a high Sm deposit
content of 32 at % from a bath consisting of 1M Sm sulfamate, 0.05M
Co sulfate, 0.15M glycine at 60.degree. C. At low CD of 10 & 50
mA/cm.sup.2 and 25.degree. C., increasing solution pH increased Sm
deposit content and then reached a constant. At 60.degree. C., Sm
content increased with increased solution pH and at 100 and 300
mA/cm.sup.2, Sm content reached maximum at pH 5 and 4,
respectively. Rotating disk electrode (RDE) results suggest mass
transfer effects in the deposition of Co.
[0428] Decreased Sm sulfamate concentration increased Sm deposit
content. However, high content of Sm hydroxide/oxide was found
indicating that the increase of Sm content was due to formation of
Sm hydroxide/oxide in deposits. Highest Sm contents were obtained
at glycine concentration between 0.1M (glycine: Co.sup.2+=2:1) and
0.15M (glycine: Co.sup.2+=3:1). Addition of NH.sub.4 sulfamate
resulted in decreased Sm content.
[0429] Crystal structures were dependent on Sm content. Deposits
changed from crystalline to non-crystalline structures by increased
Sm deposit content. Crystal structures of electrodeposited Co--Sm
crystallites were dominated by hcp phases. Higher Sm content
deposits were usually accompanied with more microcracks due to
higher internal stress by lattice distortion. Lower microcrack
densities were found in the deposit obtained at higher solution
temperatures.
[0430] Magnetic properties of electrodeposited Co--Sm alloys are
strongly dependent on alloy composition, crystal structure and
particle size of deposits. Increased Sm content resulted in
deposits changing from crystalline to non-crystalline structures
and decreased grain size. Magnetic saturation (Ms) decreased
linearly with increased Sm deposit content and was in agreement
with sputtered films. On the other hand, deposits with high
oxide/hydroxide content had much lower Ms values. For deposits
obtained at different conditions, perpendicular coercivity varied
in the range of 150 to 1160 Oe, and parallel coercivity fluctuated
between 50 and 150 Oe. Hc decreased sharply but changed little in
the in-plane direction by increase in Sm content. The significant
change in Hc may be the result of the considerable decrease in
particle size in the in-plane direction. Parallel squareness
(Mr/Ms) were higher than perpendicular squareness indicating the
preferred magnetization direction lies on the deposit plane.
Squareness decreased with increased Sm content for deposits
changing from crystalline to non-crystalline structures.
[0431] In Hull Cell studies, we have already learned about how
electrodeposition parameters qualitatively affected Sm deposit
content and CD.sub.max (the maximum CD for metallic deposits
region) by Hull cell study. In addition, proper plating solutions
and operating conditions of obtaining high Sm content deposit (26
at % Sm) by DC electrodeposition have also been achieved. In DC
electrodeposition studies, we not only made deposits by parallel
electrodes to confirm the Hull cell results but also studied the
impacts of these parameters on the properties of electrodeposited
Co--Sm alloys. Alloy properties, such as composition, crystal
structure, morphology, microstructure and magnetic properties (i.e.
coercivity Hc, saturation magnetization Ms and squareness S),
varied by DC electrodeposition parameters will be studied and
correlated. These studies are very helpful for not only getting a
better understanding about the dependence of alloy properties on
electrodeposition parameters but also providing important
information to develop the mechanism or the electrodeposition of
Co-Sin alloys in the future.
[0432] To understand the magnetic behavior of the electrodeposited
Co--Sm thin films, it is necessary to study the dependence of
Co--Sm alloy composition on operating conditions (i.e., current
density, solution temperature, solution pH, and fluid dynamics) and
plating solutions (i.e., concentration of Sm sulfamate, glycine,
NH.sub.4 sulfamate and types of supporting electrolytes) and the
dependence of morphology (i.e. roughness, cracks and pitting),
crystalline (i.e., crystal structure, orientation, grain size and
microstructure) on these parameters, then correlate these
properties to the magnetic behaviors of electrodeposited
deposits.
[0433] At the beginning of each section, the effect of parameter on
alloy composition and current efficiency will be quantitatively
measured and analyzed. The amount of Co and Sm deposition and
H.sub.2 gas evolution will be showed in normalized charge diagrams.
The second part mainly focused on the effect of parameters on
crystal structures, orientations, grain size, morphologies and
microstructures of deposits by their XRD patterns and the SEM
micrographs. Finally, the effect of parameters on deposit magnetic
properties (i.e., Hc, Ms and S) obtained from hysteresis loops of
deposits will be studied and correlated to the other alloy
properties discussed in the first and the second part. Magnetic
properties of CoSm alloys as deposited will be revealed in this
study.
[0434] The goals of the parametric studies of DC electrodeposition
were: Confirming Hull cell results and obtaining high Sm deposit
content Co--Sm alloys; Studying the dependence of alloy properties
on electrodeposition parameters; Revealing the dependence of
magnetic properties of electrodeposited Co--Sm alloys on other
alloy properties (i.e., alloy composition, crystal structures,
grain size . . . )
[0435] FIG. 59 shows the experimental flowchart of a DC experiment
which mainly includes four parts: pretreatment of cathode, DC
electrodeposition, post-treatment of specimen and characterization.
Setup of DC electrodeposition, rotating disk electrode, design of
experiments, pretreatment and post-treatment and characterization
and analysis of specimens will be described in the following
discussion.
[0436] a. Setup of DC Electrodeposition
[0437] FIG. 60 shows the setup of a DC electrodeposition system. An
EG&G PAR potentiostat, model 173, served as the power source
for electrodeposition. A coulometer to measure the total applied
charge passed during the electrodeposition. The deposits were
obtained in a 250 mL beaker filled with the plating solution.
Tapped brass panels with 3.8 cm.sup.2 (2.times.1.9 cm) deposit area
served as cathodes and a platinum sheet (3.times.6 cm) was used as
the anode; in this experiment, the distance between the cathode and
the anode is 4 cm. A saturated calomel electrode (SCE) served as a
reference electrode to measure the cathodic potential during the
electrodeposition process. A shielding panel with a 2.times.2 cm
opening window, designed by the simulation result of ANSYS (a
finite element analysis software), was placed between the cathode
and anode to minimize the thickness variation of deposit by
uniformizing the current density distribution on the cathode.
[0438] b. Setup of Rotating Disk Electrode (RDE) System
[0439] The setup of a RDE system shows in FIG. 61. A brass disk
(diameter of 6.4 mm) was inserted into the cavity at the bottom of
the Teflon rod; a copper rod was inserted into that Teflon rod from
the other side and all the way down to touch the back side of the
brass disk to make electrical contact. The RDE was jointed with a
stainless rod by a coupler, and the stainless rod was rotated by a
motor through a transmission belt. The RDE was dipped into the
electrolyte with the brass disk facing down to the Pt panel located
at the bottom of the plating cell. The distance between cathode and
anode is about 2 cm. A SCE served as a reference electrode to
measure the cathodic potential during electrodepositions.
[0440] C. Design of Experiments
[0441] In the study of DC electrodeposition, operating conditions,
such as current density, temperature, pH, fluid dynamics will be
varied. Various current densities (2-500 mA/cm.sup.2), bath
temperatures (25-60.degree. C.), pH values of plating solutions
(2-6), fluid dynamics (RDE. 0-4000 rpm) were used to obtain
deposits. Furthermore, composition of plating baths, such as the
concentrations of samarium sulfamate as metal ions, glycine as
complexer, and ammonium sulfamate, ammonium chloride and potassium
chloride as conducting salts will be varied for different
concentrations to examine their effects on electrodeposited
cobalt-samarium alloys. The concentration of cobalt sulfate was
constant at 0.05M. Plating baths used to obtain deposits are showed
in Table 20:
TABLE-US-00020 TABLE 20 Plating baths of cobalt-samarium alloys
Item Bath Sm sulfamate Co sulfate Glycine NH.sub.4 Sulfamate
NH.sub.4Cl KCl pH 1 1 1 M 0.05 M 0.15 M 5.7 2 6 1 M 0.05 M 5.9 3 9
1 M 0.05 M 0.15 M 5.0 4 10 1 M 0.05 M 0.15 M 4.0 5 11 1 M 0.05 M
0.15 M 3.0 6 12 1 M 0.05 M 0.15 M 2.0 7 13 0.75 M 0.05 M 0.15 M 5.8
8 14 0.5 M 0.05 M 0.15 M 5.9 9 15 0.25 M 0.05 M 0.15 M 5.9 10 16 1
M 0.05 M 0.05 M 5.9 11 17 1 M 0.05 M 0.10 M 5.8 12 18 1 M 0.05 M
0.20 M 5.7 13 19 1 M 0.05 M 0.50 M 5.5 14 8 1 M 0.05 M 0.15 M 1 M
5.2 15 20 1 M 0.05 M 0.15 M 0.75 M 5.3 16 21 1 M 0.05 M 0.15 M 0.5
M 5.4 17 22 1 M 0.05 M 0.15 M 0.25 M 5.4 18 23 1 M 0.05 M 0.15 M 1
M 5.5 19 24 1 M 0.05 M 0.15 M 1 M 5.6 (The pH values of the plating
baths were measured at 25.degree. C.; the pH values of bath 9, 10,
11 and 12 were adjusted by sulfamic acid.)
[0442] Bath 12, 11, 10, 9 and 1 were used to study the effects of
pH from 2 to 6; bath 15, 14, 13 and 1 were used to study the
effects of the concentration of samarium sulfamate from 0.25 to 1M;
bath 18, 19. 1, 16 and 17 were used to study the effects of the
concentration of glycine from 0.05 to 0.5 M; bath 1, 22, 21, 20 and
8 were used to study the effects of the concentration of ammonium
sulfamate from 0 to 1 M; bath 8, 23 and 24 were used to study the
effects of different types of conducting salts in the plating
baths.
[0443] d. Pretreatment and Post-Treatment
[0444] Before electrodeposition, the brass panels were mechanically
cleaned, soaked in 0.1M NaOH solution for 10 min., rinsed in
deionized water, immersed in 10% HCl for 30 seconds and than rinsed
with deionized water. Unless otherwise noted, the total charge
passed was 50 coulombs; solutions were not agitated during
electrodeposition (except in the rotating disk electrode, RDE).
[0445] After the deposition of Co--Sm alloys for 50 coulombs, the
deposits were removed from plating solution, rinsed with deionized
water, and dried with nitrogen gas. Disk-shaped specimens of
diameter of 6.4 mm (specimen area=31.7 mm.sup.2) were die-punched
out from deposits for analysis.
[0446] e. Characterization and Analysis
[0447] The samarium
Sm Sm + Co ( at % ) ##EQU00007##
and cobalt deposit content
Co Sm + Co ( at % ) ##EQU00008##
were determined by an energy dispersive x-ray spectroscopy (EDS)
with a Kevex detector in a Cambridge SEM (see characterization
section in Hull Cell studies); the mass of deposited cobalt was
measured by a PerkinElmer flame atomic absorption spectrometer (AA,
mode 631); the crystal structure, orientation, phase identification
and grain size were determined by a PANalytical x-ray diffraction
system (XRD, model X'Pert Pro) (see characterization section in
Hull Cell studies); the surface morphology, microstructure and
grain size were observed by a JEOL scanning electron microscopy
(SEM, model JSM-6700F); magnetic properties were determined by a
ADE Tech. vibrating sample magnetometer (VSM, model 1660). Unless
otherwise noted, the experimental data presented in discussion
sections are restricted to deposits with a metallic appearance.
[0448] f. Flame Atomic Absorption Spectroscopy (AA)
[0449] The specimen was dissolved by nitric acid than diluted with
deionize water to 50 mL as the analytical solution for FAAS. By
FAAS, the lowest cobalt concentration can be detected (limit of
quantitation, LOQ) is 1 ppm; the concentration depart from
linearity (limit of linearity, LOL) is 5 ppm. If the cobalt
concentration of solution was out of applicable range (1-5 ppm),
solution will be properly diluted or concentrated and the
measurement was repeated. The Co concentration of the solution can
be calculated from its absorption referring to the calibration
curve. The mass of cobalt WCo in the specimen can be obtained by
solution concentration and volume.
[0450] Calculation of the mass of Sm (W.sub.51,) and current
efficiency (CE): The mass of Sm in the specimen Wsm can be
calculated by:
W Sm = W Co Sm ( wt % ) Co ( wt % ) ( Equation 4 ) ##EQU00009##
where Wco was obtained by AA and the Sm and Co content were from
EDS.
[0451] Calculation of the current efficiency (CE): The current
efficiency (CE) can be calculated by the charge used to obtain
metal (Sm and Co) divided by the charge (50 coulombs) passes during
the electrodeposition. The charge used to obtain Sm and Co can be
calculated by:
C = C Co + C Sm = F ( W Co Z Co 2 + M Co + W Sm Z Sm 3 + M Sm ) (
unit : coulomb ) ( Equation 5 ) ##EQU00010##
where C is the charge used to obtain metal (Co and Sm); Z is the
valance of the metal ion (ZCO.sup.2+=2 and Zsm=3); F is Faraday's
constant, the charge carried by a mole of electrons=96,500 C/mol; M
is the atomic mass (M.sub.Co=58.93 g and M.sub.Sm=150.36 g); W is
the mass of elements in the specimen. The calculation of CE assumed
the Sm and Co in deposit were obtained from charge transfer
reactions (the reduction of Co.sup.2+ and Sm.sup.3+) rather than
chemical reactions (the precipitation of Co(OH).sub.2 and
Sm(OH).sub.2). The electrons passed during the electrodeposition
were used only on the reduction of Sm, Co and H.sub.2. This
experimental assumption provided a first approximation of CE in
Co--Sm electrodeposition.
[0452] g. Scanning Electron Microscopy (SEM)
[0453] SEM provides specimen surface images by collecting the
secondary or back scattering electrons emitted from specimen after
the electron bombardment [P. J. Goodhew, J. Humphreys and R.
Beanland, Electron microscopy and analysis (3rd edition), Taylor
& Francis, (2001), pp. 196-205]. These images were used to
study the topography, morphology and microstructure of
electrodeposited Co--Sm alloys obtained from different solution and
operating conditions.
[0454] h. Vibrating Sample Magnetometer (VSM)
[0455] VSM [D. Jiles, Introduction to magnetism and magnetic
materials, Chapman & Hall, New York, (1991), pp. 47-53], a
gradiometer measuring the magnetic induction difference
with/without the specimen, gives a direct measurement of the
magnetization (M) under applied magnetic field (H). A schematic of
a typical VSM is shown in FIG. 62.
[0456] The disk shaped specimen was placed on a quartz sample
holder and was vibrated with fixed frequency in C-C' direction. The
magnetic field was applied parallel (A-A' direction) and
perpendicular (B-B' direction) to film plane to obtain in-plane and
perpendicular magnetic properties, respectively. The magnetic field
swept between ''10,000 and 10,000 Oe was used to obtain the
hysteresis loop shown in FIG. 63.
[0457] Important magnetic properties of electrodeposited Co--Sm
alloys can be obtained from its hysteresis loop as follows: He
(Coercivity): the magnetic field needed to reduce the magnetic
induction to zero after the material has been saturated (fully
magnetized). Ms (Saturation Magnetization): maximum magnetization
obtained in the hysteresis loop. Mr (Remanence): magnetization at
applied magnetic filed equals to zero. Squareness (or the reduced
remance): Mr/Ms. BHmax (Maximum Energy Product): the energy
required to demagnetize a permanent magnet.
[0458] i. Effect of CD and Solution Temperature
[0459] Alloy Composition: Samarium deposit content (at %) increased
with increasing current density (CD). CD.sub.max (the highest CD to
obtain metallic deposits) was extended by elevated solution
temperatures (FIG. 64(a)). At 25.degree. C., CD.sub.max was limited
to 50 mA/cm.sup.2 (Sm=14.5 at %), whereas for a solution
temperature of 60.degree. C., CD.sub.max increased to 500
mA/cm.sup.2, resulting in deposit Sm content of 32.1 at %.
Depending on CD and solution temperature, deposits of Sm content
between 0 and 32 at % could be obtained from bath 1 (1 M Sm
sulfamate, 0.05M Co sulfate, 0.15M glycine) which satisfies the
stoichiometric compositions of intermetallic Sm.sub.2Co.sub.17
(10.5 at %) and SmCo.sub.5 (16.7 at %) and, in addition,
Sm.sub.2Co.sub.7 (22.2 at %) and SmCo.sub.3 (25 at %). Therefore,
Co--Sm alloys of sufficient Sm content for Sm--Co magnets (i.e.
Sm.sub.2Co.sub.17 and SmCo.sub.5) can be produced by
electrodeposition.
[0460] Current efficiency (CE) calculated from the charge needed to
obtain metals (i.e. Sm and Co) divided by the total charge passed
in electrodeposition (50 coulombs). CE dropped sharply between 2
mA/cm.sup.2 (66%) and 100 mA/cm.sup.2 (20%) with little change
between 100 mA/cm.sup.2 and 500 mA/cm.sup.2 in the 60.degree. C.
solution, whereas the CE decreased almost exponentially in the
25.degree. C. electrolyte, as shown in FIG. 64(b). CEs were higher
at elevated solution temperatures.
[0461] To show individual changes in reduced products in
electrodepositions, a nomialized charge plot is provided in FIG.
65. Normalized charge or charge ratio indicates the
electroreduction of a specified species. Calculation of normalized
charges was based on two assumptions. First, all electrons supplied
to the cathode contributed to the production of Sm, Co and H.sub.2
only; reduction of glycine or other species were ignored. Second,
Sm and Co in deposits were obtained by electroreduction of
reactants (ions) at the cathode.
[0462] Precipitates of Sm(OH).sub.3 and Co(OH).sub.2 were not
considered. Normalized charges of Sm and Co were calculated from
charges required to obtain the respective metals in the deposits
divided by the total charge passed (50 coulombs). Normalized charge
of H.sub.2 was obtained by difference (subtracting charges to
produce Sm and Co from the total charge).
[0463] From the variation of normalized charges with CD, as shown
in FIG. 7, at 60.degree. C., increased CD (from 2 to 500
mA/cm.sup.2) resulted in a sharp increase in Sm from 0.01 to 0.09
and a decrease in Co from 0.65 to 0.13 leading to a substantial
increase in Sm deposit content from 1.3 to 32.1 at % (FIG. 64(a)).
At 25.degree. C., increased Sm deposit content from 3 to 15 at %
with increasing CD from 2 to 50 mA/cm.sup.2 was due to a sharp
decrease in Co (normalized charge from 0.5 to 0.07) and a slight
change in Sm from 0.02 to 0.03.
[0464] The cathode potential was measured at various CDs and
solution temperatures with a saturated calomel electrode (SCE)
serving as the reference electrode. In alloy electrodeposition, the
cathode potential can affect the composition of deposits [N. Ibl,
Surf Tech., 10, 81, (1980)]. In addition, the cathode potential may
change the nucleation rate (grain size) [M. Paunovic and M.
Schlesinger, Fundamentals of electrochemical deposition, John Wiley
& Son, Inc., New York, (1998), pp. 107-121], microstructures
[H. Seiter, H. Fischer, and L. Albert. Electrochim. Acta, 2, 97
(1960)], and phases and orientation [N. A. Pangarov, J.
Electroanal. Chem., 9, 70, (1965); N. A. Pangarov and S. D.
Vitkova, Electrochim. Acta, 11, 1733, (1966)] of deposits. These
characteristics govern magnetic properties of deposits. FIG. 66(a)
shows the polarization curves of Co--Sm electrodeposition from bath
1 at various solution temperatures.
[0465] Lower solution temperatures resulted in more negative
cathode potentials in the electrodeposition of Co--Sm alloys. The
dependence of Sm deposit content on cathode potentials is shown in
FIG. 66(b). A higher Sm content was obtained at more negative
cathode potentials. A linear relationship was found between Sm
deposit content and the cathode potential, combining the effects of
CD and solution temperatures.
[0466] It should be noted that the co-deposition of Sm and Co was
observed at cathode potentials much less negative than the
equilibrium potential of Sm (E.degree.Sm/Sm.sup.2+=-2.65 V vs SCE)
[W. M. Latimer, The oxidation states of the elements and their
potentials in aqueous solution, Prentice Hall, N.Y., (1953), p
289]. This result indicates the co-deposition mechanism is more
complex than the direct electrodeposition of both Co and Sm from
their respective aqueous ionic forms.
[0467] j. Crystal Structure
[0468] The dependence of crystal structures on CD and solution
temperature was determined by XRD. FIG. 67 and FIG. 68 show XRD
results of deposits obtained from bath 1 at various CDs and at 25
and 60.degree. C., respectively. It is noted that increased CD
resulted in deposits changing from crystalline (or
semi-crystalline) to non-crystalline; no diffraction peaks of Co,
Sm or Co--Sm intermetallics were found between 10 and 50
mA/cm.sup.2 at 25.degree. C. and Sm or Co--Sm intermetallics
between 2 and 500 mA/cm.sup.2 at 60.degree. C.; Co peaks
disappeared at 60.degree. C. and 500 mA/cm.sup.2. Crystal
structures of electrodeposited Co--Sm crystallites were dominated
by .alpha.-Co (hcp) phases; neither .beta.-Co (fcc) nor Sm
(rhombohedral) phases were found in deposits.
[0469] At 25.degree. C. (FIG. 67), (10.0), (00.2), (10.1) and
(11.0) peaks of .alpha.-Co and very weak (20.1) peak of SmCo.sub.5
(hexagonal) and (20.2) peak of Sm.sub.2Co.sub.17 (hexagonal) were
observed at 2 mA/cm.sup.2 (Sm=3 at %). In addition, weak (11.0)
peaks of Sm(OH).sub.3 were found in the deposits at 25.degree. C.,
but not at 60.degree. C. (see FIG. 68).
[0470] At 60.degree. C. (FIG. 68), a strong (00.2) peak of a-Co was
observed at 2 mA/cm.sup.2 decreasing with further increased CD at
10 and 25 mA/cm.sup.2. Mixed orientations of (10.1), (11.0) and
(10.0) peaks appeared from 10 (Sm 2.3 at %) to 100 mA/cm.sup.2
(Sm=9.2 at %). The (00.2) peak disappeared at 50 mA/cm.sup.2.
Crystalline peaks were not seen at 500 mA/cm.sup.2 (Sm=32.1 at
%).
[0471] Effect of solution temperature on deposit crystal structures
at various CDs (2, 25 and 50 mA/cm.sup.2) are compared in FIG. 69.
At higher CDs (25 and 50 mA/cm.sup.2), decreased solution
temperatures changed deposits from crystalline to non-crystalline
structures, similar to the effect of the increase of CD on deposit
crystal structures (see FIG. 68 & FIG. 69). At low CD (2
mA/cm.sup.2), the decrease of solution temperature from 60 (Sm=1.3
at %) to 25.degree. C. (Sm=3 at %) resulted in the decrease of
.alpha.-Co (00.2) peak intensity, and other a-Co orientations (i.e.
(11.0), (10.0) and (10.1)) were observed at 25 and 40.degree. C.
These orientations were also seen at 60.degree. C., and both 10 and
25 mA/cm.sup.2 (FIG. 68).
[0472] According to these XRD results, the change in deposit
orientation follow the same trend as varying CD or solution
temperature and are related to Sm deposit content (or cathode
potential). Thus, XRD results are organized by dependence of cc-Co
orientation on Sm deposit content at various CDs and solution
temperatures in Table 21. Higher solution temperatures required
higher Sm content to produce non-crystalline deposits.
TABLE-US-00021 TABLE 21 Dependence of XRD patterns on Sm deposit
content at various CDs and solution Deposit Current Density
(mA/cm.sup.2) T (.degree. C.) Properties 2 10 25 50 100 200 300 500
550 60 hcp peaks (00.2) s (00.2) m (00.2) w (10.1) w (10.1) w
(11.0) w (10.0) w non- non- (10.1) w (10.1) m (11.0) w (11.0) w
(10.0) m crystalline metallic (11.0) m (11.0) w (10.0) m (10.0) m
(10.0) m (10.0) m Sm (at %) 1.3 2.3 5.4 7.4 9.2 11.2 16.7 32.1 40
hcp peaks (00.2) m (00.2) w (11.0) w (10.0) w non- non-
non-metallic (10.1) w (10.1) w (10.0) w crystalline crystalline
(11.0) m (11.0) w (10.0) m (10.0) w Sm (at %) 1.3 6.2 7.7 8.3 13.0
18.2 25 hcp peaks (00.2) w non- non- non- non-metallic (10.1) w
crystalline crystalline crystalline (11.0) s (10.0) s Sm (at %) 3.0
6.5 9.5 14.5 weak Sm(OH).sub.3 (10-50 mA/cm.sup.2 at 25.degree.
C.), Sm.sub.2Co.sub.17 and SmCo.sub.3 (2 mA/cm.sup.2 at 60.degree.
C.) peaks were not included s, m and w compared the intensity of
peaks, "s" = strong, "m" = medium, "w" = weak non-crystalline
defined as no a-Co peaks was found in XRD
[0473] As shown in FIG. 66(b), Sm deposit content can be correlated
to the cathode potential. Therefore, it is important to analyze the
change in orientation with cathode potential. According to
Pangarov's calculation for hcp lattice [N. A. Pangarov, J.
Electroanal. Chem., 9, 70, (1965)] in electrodeposition, an [00.1]
orientation should be expected at very low overpotentials, and with
increase in overpotential, the following orientation should appear:
[10.1], [11.0], [10.0] and [11.2]. Later on, the experimental
results [N. A. Pangarov and S. D. Vitkova, Electrochim. Acta, 11,
1733, (1966)] of electrodeposited Co (sulfate bath, pH5,
1580.degree. C., 10-200 mA/cm.sup.2) were provided.
Electrodeposited Co obtained at low overpotential (high solution
temperatures and low CDs) resulted in a pure [00.1] orientation.
Medium overpotential (at low solution temperatures) leads to [11.0]
and [10.0] as a mixed orientation. High overpotential, low solution
temperatures and high CDs, had [10.0] orientation; [10.1]
orientation was included with other orientation.
[0474] The dependence of orientation of electrodeposited Co--Sm
alloys is similar to electrodeposited hcp Co as strongly related to
CD, solution temperature, Sm content (or cathode potential) in
agreement with Pangarov's calculation of the hcp lattice and his
experimental results of hcp Co deposition.
[0475] k. Distortion of HCP Lattice
[0476] For more carefully studying the XRD patterns obtained at
60.degree. C. from bath 1, Bragg angles (2.THETA.B of hcp-Co (00.2)
and (10.0) peaks were found varying with Sm deposit content (FIG.
119). Increased Sm deposit constant resulted in the decrease of
Bragg angle of (00.2) plane from 44.425.degree. (point c) to
44.179.degree. (point d) for Sm content increased from 1.3 to 2.3
at %. On the other hand, Bragg angle of (10.0) plane increased from
41.643.degree. (point a) to 41.798.degree. (point b) for Sm content
increased from 2.3 to 16.7 at %.
[0477] Lattice constants of these deposits were calculated and
compared to pure Co in Table 22. After comparing lattice constants
of deposits of different Sm content, it was observed that lattice
constant a (parallel to the basal plane of hcp structure) decreased
with increased Sm deposit content, whereas lattice constant c
(perpendicular to the basal plane of hcp structure) increased.
Changed lattice constants implied the distortion of hcp Co lattice
by adding Sm atoms into Co matrix. The radii of Co and Sm atoms are
quite different; the atomic radius of Co is 1.25 A and Sm is 1.81 A
[J. P. Schaffer, A. Saxena, S. D. Antolovich, T. H. Sanders, S. B.
Warner, The science and design of engineering materials,
McGraw-Hill Componies, Inc, New York, (1999), p 773 .sup.I.degree.
Centre d'information du cobalt, Cobalt monograph, 35, Rue Des
Colonies, Brussels, Belgium, (1960), p75]. The size misfit
R Sm - R Co R Co = 45 % ##EQU00011##
between Sm and Co could cause Co lattice distortion by adding Sm
atoms. The distortion caused by addition of Sm tended to elongate
Co lattice along the c-axis and compress along the basal plane.
Furthermore, such a distortion of Co lattice may generate internal
stress leading to microcracks in deposits. This will be discussed
in the next section.
TABLE-US-00022 TABLE 22 Dependence of Bragg's angles (219) of
(10.0) and (00.2) planes and lattice constants of electrodeposited
Co-Stn alloys on Sm deposit content Bragg's Angle
(2.crclbar..sub.B) Lattice Constant CD Sm Content (deg.) (.ANG.)
(mA/cm.sup.2) (at %) (10.0) (00.2) a c -- Pure Co 41.595* 44.528*
.sup. 2.507.sup.10 .sup. 4.069.sup.10 2 1.3 41.643 44.425 2.504
4.078 10 2.3 -- 44.179 -- 4.100 50 7.4 41.686 -- 2.502 -- 300 16.7
41.798 -- 2.495 -- *Bragg angles of pure Co (hep) (10.0) and (00.2)
peaks were calculated from the lattice constants of pure Co.sup.10
by Bragg's law (1) and the relationship between lattice constants
and interplanar spacing of (hkl) plane of hep structure (2) 2 d hkl
sin .theta. B = .lamda. ( 1 ) 1 ( d hkl ) 2 = 4 3 ( h 2 + hk + k 2
a 2 ) + l 2 c 2 ( 2 ) ##EQU00012## where .lamda. (CuK.sub..alpha.)
= 1.54184.ANG..crclbar..sub.e: Bragg's angle of (hkl)
planed.sub.hkl: interplanar spacing of (hkl) plane ##STR00001##
[0478] 1. Morphologies and Microstructures
[0479] SEM pictures in FIG. 70 and FIG. 71 show the dependence of
morphology and microstructure on CD at 25 and 60.degree. C.,
respectively. FIG. 72 and FIG. 73 compare the effect of solution
temperature at 25 and 50 mA/cm.sup.2, respectively. The increase in
Sm content due to increased CD (FIG. 70 & FIG. 71) or decreased
solution temperature (FIG. 72 & FIG. 73) resulted in more
microcracks and smaller particle sizes.
[0480] Microstructures of crystalline deposits were fiber-shaped
nano-rods. With increased Sm content, deposits changed to
non-crystalline structures (XRD results) consisting of tiny
roundish particles.
[0481] Microstructures of crystalline deposits of Co--Sm alloys are
similar to electrodeposited Co. According to Cavallotti et al [P.
L. Cavallotti, E. Galbiati and T. Chen, in Electroplating
Engineering and waste Recycle, D. D. Snyder, U. Landau, R. Sard
(Eds.), ECS Pub., Pennington, N.J., 130, (1983)], celluar
electrodeposited Co was obtained from pH 6.5 sulfamate or sulfate
solutions and changed to dendritic growth by increasing CD.
Outgrowing basal planes with "needle-shaped crystalline particles"
were found in deposits at 100 mA/cm.sup.2 and 50.degree. C. In
addition, they found that the crystallite size was mainly
influenced by CD and solution temperature [P. L. Cavallotti, E.
Galbiati and T. Chen, in Electroplating Engineering and waste
Recycle, D. D. Snyder, U. Landau, R. Sard (Eds.), ECS Pub.,
Pennington, N.J., 130, (1983)]. Increasing solution temperature
increased grain size from tens of nanometers to several hundred
nanometers. Increasing CD, the grain size decreased. Similar
results of the change in grain size with CD and solution
temperature were observed in electrodeposited Co--Sm alloys.
[0482] Particle size changed with CD, solution temperature and Sm
contents. Particle size was measured and presented in Table 23 and
FIG. 74. The results provided average values of particle size to
illustrate the tendency rather than exact values at operating
conditions. Because most of the deposit microstructures were
fiber-shaped nano-rods lying on the film plane, their lengths were
much larger than widths and heights and were measured individually.
Particle lengths (.sigma..sub.L) and widths (.sigma..sub.W) in the
in-plane direction were determined by SEM; seven particles were
sampled and measured from a SEM picture under an operating
condition, and an average of particle size in the in-plane
direction (.sigma..sub..parallel.) was the arithmetic average of
the particle length and width. Particle thickness
(.sigma..sub..perp.) (perpendicular to film plane) was calculated
by the Scherrer's equation according to FWHM of .alpha.-Co (10.0)
peaks in XRD patterns and represent the particle size in the
perpendicular direction.
TABLE-US-00023 TABLE 23 Dependence of particle site on Sm deposit
content at various CDs and solution temperatures T Current Density
(mA/cm.sup.2) (.degree. C.) Particle Size (nm) 25 50 100 300 500 60
Length .sigma..sub.L 575 500 450 300 63 Width .sigma..sub.W 25 20
18 13 14 .sigma..sub.|| = (.sigma..sub.L + .sigma..sub.W)/2 300 260
234 158 38 Thickness, .sigma..sub..perp. 22 18 15 10 -- Sm (at %)
5.4 7.4 9.2 16.7 32.1 Crystal Structure crystalline non-
crystalline 40 Length .sigma..sub.L 440 205 95 non-metallic Width
.sigma..sub.W 22 18 16 .sigma..sub.|| = (.sigma..sub.L +
.sigma..sub.W)/2 231 111 55 Thickness, .sigma..sub..perp. 20 17 --
Sm (at %) 7.7 8.3 13.0 Crystal Structure crystalline non-
crystalline 25 Length .sigma..sub.L 80 60 non-metallic Width
.sigma..sub.W 18 13 .sigma..sub.|| = (.sigma..sub.L +
.sigma..sub.W)/2 49 37 Thickness, .sigma..sub..perp. -- -- Sm (at
%) 9.5 14.5 Crystal Structure non-crystalline Length .sigma..sub.L
and width .sigma..sub.W of particles (in-plane direction) are
measured by SEM Thickness, .sigma..sub..perp. of particles
(perpendicular direction) are calculated by Scherrer's equation
according to .alpha.-Co (10.0) peaks in XRD -- means no .alpha.-Co
(10.0) peaks found in XRD pattern non-crystalline deposit)
[0483] Increased Sm deposit content leads to decrease in particle
size, and the change was more significant in the in-plane direction
mainly due to the reduction of the particle length. For deposits of
similar Sm content, higher solution temperatures resulted in larger
particle sizes in the in-plane direction (.sigma..sub..parallel.),
whereas particle size in the perpendicular direction
(.sigma..sub..perp.) varied little with solution temperature. From
the view point of nucleation and growth theory of
electrocrystallisation, higher current density resulted in a higher
nucleation rate [J. C. Puippe and F. Leaman, Theory and practice of
pulse plating, American electroplaters and surface finishers
society, Orlando, Fla., (1986), pp. 17-39] reducing the average
distance between crystallites, therefore, a decrease in particle
size can be expected.
[0484] m. Magnetic Properties
[0485] The most important characteristics governing the quality of
electrodeposited hard magnetic films (i.e. coercivity Hc,
saturation magnetization Ms and squareness Mr/Ms) are grain size,
crystal structure and orientation and the presence of alloying
elements [L. T. Romankiw and D. A. Thompson, in Magnetic properties
of plated films in Properties of Electrodeposits: Their
Measurements and Significance, Electrochemical Society, Princeton,
N.J. (1975), pp 389-426]. Magnetic hysteresis loops of deposits
obtained at various CDs and solution temperatures were measured by
VSM for an applied magnetic field scanning between -10K and 10K Oe.
In-plane (.mu.) and perpendicular (.perp.) measurements represent
the magnetic field applied parallel and perpendicular to the film
plane, respectively. Magnetic properties of Hc, Ms and squareness
were obtained from hysteresis loops.
[0486] FIG. 75 gives examples of hysteresis loops obtained at 25
and 60.degree. C. and at various CDs. It was noted that
magnetizations (Ms) were easier in the in-plane direction than the
perpendicular direction indicating the easy-axis (EA) along the
in-plane direction and the hard axis (HA) along the perpendicular
direction. At 25 and 60.degree. C., Ms.sub..parallel. were higher
than Ms.sub..perp., and they approached each other sooner as
magnetic field increased. Ms.sub..parallel. is used for the
following discussion regarding approaching magnetization
saturation. On the other hand, Hc.perp. were higher than
Hc.sub..parallel., and they got closer to each other as CD
increased. At 25 and 60.degree. C., Ms and Hc.perp. decreased as CD
increased. At constant CD, Ms and He increased as solution
temperature increased from 25 to 60.degree. C. These results can be
correlated to the alloy compositions and crystal structures of
deposits. When deposits changed from crystalline to non-crystalline
structures with increased Sm content by increased CD, magnetic
properties of deposits appeared more isotropic where the Ms.perp.
were closer to Ms.sub..parallel. and the Hc.perp. were closer to
Hc.sub..parallel. Ms and Hc.perp. decreased with increased Sm
deposit content. The dependence of Ms and He on alloy composition
and deposit crystal structure were observed in these hysteresis
loops.
[0487] To further quantify the dependence of magnetic properties on
alloy composition and deposit characteristics, particle size,
crystal structures, Hc, Ms, and squareness of deposits were
correlated to Sm content in FIG. 76.
[0488] For the electrodeposited Co--Sm alloys before heat
treatment, deposit characteristics (crystal structure and grain
size) were strongly dependent on Sm deposit content. With increase
in Sm deposit content, deposits changed from hcp Co crystallites to
non-crystalline structure, and grain size decreased as shown in
FIG. 76(a). Ms depended on alloy composition. Ms decreased linearly
with increased Sm deposit content and was in agreement with
sputtered films" (FIG. 76(b)). He sharply but changed little in the
in-plane direction by increase in Sm content; He.sub.t approached
Hc.sub..parallel. when deposits were of a non-crystalline structure
(FIG. 76(c)). At 60.degree. C., dependence of coercivities on Sm
deposit content (FIG. 76(c)) can be correlated to crystal structure
and particle size (FIG. 76(a)). Deposits obtained at 25 and
40.degree. C. also followed the same trend, see FIG. 74.
[0489] Hoffman has shown that the coercivity of ferromagnetic thin
films depends on crystallite size [H. Hoffman, IEEE Trans.
Magnetics, 9, 17, (1973). Smaller crystallites result in decrease
in coercivity. His prediction was later confirmed by the
experimental results of electrodeposited Co films by Armyanov et
al. [S. A. Armyanov and S. D. Vitkova, Phys. Status Solidi A, 26,
553, (1974)],[S. A. Armyanov and S. D. Vitkova, Surf Tech., 7, 319,
(1978)] who found that coercivity increased with particle size
between 20 and 400 nm. For electrodeposited Co--Sm alloys, the
in-plane particle size
((.sigma..sub..parallel.=(.sigma..sub.L+.sigma..sub.w)/2) were
larger than the perpendicular particle size (.sigma..perp.) (FIG.
76(a)) because of fiber-shaped microstructures lying on the film
plane (FIGS. 71(c), (f), (i) & (1)). For a fiber-shaped
nano-rod lying on the film plane along the in-plane magnetic field
(FIG. 77(b)), should consider the average particle size intersected
by the in-plane magnetization,
(.sigma..perp.+.sigma..sub.w)/2.apprxeq..sigma..sub..parallel..
Hc.perp. should consider the average particle size intersected by
perpendicular magnetic field,
(.sigma..sub.L+.sigma..sub.w)/2=.sigma..sub..parallel.. For those
fiber-shaped nano-rods lying on the film plane but not along the
in-plane magnetic field, the average particle sizes intersected by
in-plane magnetization are between (.sigma..perp.+.sigma..sub.w)/2
and (.sigma..perp.+.sigma..sub.L)/.sup.2 depending on the angle
between the fiber axis and in-plane magnetic field.
[0490] The sharp reduction in Hci with increased Sm content (FIG.
76(c)) can be correlated to the significant decrease in
.sigma..sub..parallel. (FIG. 76(a)). On the other hand,
.sigma..perp. decreased little by increased Sm content resulting in
a small change in Hc.sub..parallel.. Larger .sigma..sub..parallel.
than .sigma..perp. could explain higher Hc.perp. than
Hc.sub..parallel. of these deposits. When deposits became
non-crystalline consisting of tiny roundish particles (FIG. 70(i)
and FIG. 71(o)), Hc.perp. was closer to Hc.sub..parallel. because
of similar .sigma..sub..parallel. and .sigma..perp. values. The
coercivity of electrodeposited Co--P alloys and Co metal also
depend on crystal structure of deposits [K. Miller, M. Sydow and G.
Dietz, Magn. Magn. Mater., 53, 269, (1985)]; increasing P content
leads to a change from crystalline to non-crystalline deposits, and
coercivity decreased significantly. For electrodeposited Co--Sm
alloys, increased Sm content also resulted in deposits changing
from crystalline to non-crystalline (FIG. 76(a)). This can cause
the decreased coercivities.
[0491] The squareness ratio (Mr/Ms) of deposits provides the
preference of magnetization direction. For example, magnetization
direction is closer to the in-plane direction when in-plane
squareness is higher. For ferromagnetic materials, the
magnetization direction strongly depends on the minimization of the
total magnetic energy. In the absence of an external magnetic
field, magnetization direction is mainly controlled by the
magnetocrystalline anisotropy energy [R. C. O'Handley, Modern
magnetic materials, John Wiley & Son, Inc., New York, (2000),
pp. 179-215] and demagnetization energy [R. L. Comstock,
Introduction to magnetism and magnetic recording, John Wiley &
Son, Inc., New York, (1999), pp. 24-28]. Minimization of
magnetocrystalline anisotropy energy prefers to align magnetization
along certain crystallographic directions. In hcp crystals, the
magnetization direction prefers to align in the [00.1] direction
[R. C. O'Handley, Modern magnetic materials, John Wiley & Son,
Inc., New York, (2000), pp. 179-215]. To minimize demagnetization
energy, magnetization prefers to lie along the long axis of a
particle because demagnetization energy is proportional to the
demagnetization factor which has the smallest value in the long
axis direction of a particle [R. L. Comstock, Introduction to
magnetism and magnetic recording, John Wiley & Son, Inc., New
York, (1999), pp. 24-28]. For example, in a long cylinder particle,
demagnetization factor along this axis is zero and perpendicular to
the axis is 0.5.
[0492] As discussed in the previous section, fiber-shaped nano-rods
were found to lie on deposit surfaces (long axis of particle
aligned along the in-plane direction); particle size in the
in-plane direction is larger than the perpendicular. Higher
in-plane squareness than perpendicular can be explained by the
alignment of magnetization direction (in absence of external field)
along the long axis of particles to minimize demagnetization
energy. On the other hand, the effect of magnetocrystalline
anisotropy energy was not significant. (00.2) peaks were observed
(see Table 21: 25.degree. C.: 2 mA/cm.sup.2, 40.degree. C.: 2 and
10 mA/cm.sup.2, 60.degree. C.: 2, 10 and 25 mA/cm.sup.2) indicating
the [00.1] orientation was along the perpendicular direction in
these deposits. However, magnetization did not align along the
perpendicular direction and resulted in higher perpendicular
squareness.
[0493] Compared to the squareness of crystalline and
non-crystalline sputtered SmCos deposits, crystalline deposits have
higher squareness (0.3-0.8) than non-crystalline (-0.2) [C. Prados
and G. C. I ladjipanayis. J. Appl. Phys., 83, 6253, (1998)].
Deposits changed from crystalline to non-crystalline structure
(FIG. 76(a)) by increased Sm content indicating reduction in
squareness. Magnetic properties of non-crystalline deposits exhibit
isotropic over anisotropic (easy and hard axis caused by
crystallographic structures no longer exist). Therefore,
Hc.sub..parallel. and Hc.perp. (FIG. 76(c)) of a non-crystalline
Co--Sm deposit were quite close. The in-plane and perpendicular Ms
were also closer when deposits were non-crystalline (see FIG.
75(c), 25.degree. C. or FIG. 75(i), 60.degree. C.). On the other
hand, the in-plane squareness was still higher than perpendicular
(FIG. 76(d)) probably because the demagnetization direction is
still aligned along the in-plane direction for the reduction of
demagnetization energy. For non-crystalline deposits, particle size
in the in-plane direction is still larger than in the perpendicular
direction (see Table 21 and FIG. 74).
[0494] n. Effect of Solution pH
[0495] Alloy Composition: Solutions of various pHs were adjusted
from bath 1 by sulfamic acid to study the effect of solution pH on
Sm content and current efficiency as shown in FIG. 78.
[0496] For solution pH between 2 and 6, increased CD or decreased
solution temperature resulted in higher Sm deposit content. At low
CDs (10 & 50 mA/cm.sup.2) and 25.degree. C., increasing
solution pH increased Sm deposit content and then reached a
constant. At 60.degree. C., Sm content increased with increased
solution pH and at 100 and 300 mA/cm.sup.2, Sm content reached
maxima at pH 5 and 4. It is also important to point out that
increasing CD results in increased rate of water reduction leading
to increase in pH at cathode surface. The pH at the cathode surface
is affected by both CD and solution pH. The results in FIG. 78(a),
however, a plot of Sm content and solution pH. Estimation of the pH
at the cathode surface may be made by calculation.
[0497] According to the mechanism proposed by Schwartz et al [M.
Schwartz, N. V. Myung, and K. Nobe, J. Electrochem. Soc., 151,
C468, (2004)], a heterodinuclear complex containing Sm and Co ions
and glycine resulted in the co-deposition of Sm with Co. It is
known that the glycine structure depends on solution pH and is
considered as cationic (.sup.+H.sub.3N--CH.sub.2COOH ) at low pH,
dipolar (.sup.+H.sub.3N --CH.sub.2COO.sup.-) at medium pH
(.about.6) and anionic (H.sub.2N--CH.sub.2COO.sup.-) at higher pH;
glycine structures at different pH might alter its complexing
ability with Sm and Co ions and change the co-deposition rate or Sm
and Co.
[0498] Higher CEs were obtained at lower CDs and higher solution
temperatures at various solution pH (FIG. 78(b)). CE varied little
with solution pH compared to CD and solution temperature (FIG.
D6(b)).
[0499] o. Crystal Structure
[0500] In the previous section, it was observed that
crystalstructuress of electrodeposited CoSm alloys from bath 1 (1M
Sm sulfamate, 0.05M Co sulfate, 0.15M glycine, pH 6) were dominated
by a-Co (hcp) with some SmCos and Sm.sub.2Co.sub.17 crystallites.
Weak Sm(OH).sub.3 (11.0) peaks were found in deposits obtained at
25.degree. C., but not in deposits at 60.degree. C. Two interesting
crystal structure problems were studied by varying the pH of bath
1. First, can low pH solutions eliminate Sm(OH).sub.3 in deposits?
Second, does the decreased pH result in the hcp.fwdarw.fcc
transition which is often found in electrodeposited Co at low pH?
The second problem is not only interesting in crystallography but
also important for magnetic properties of deposits because magnetic
properties of hcp and fcc Co are quite different. For example,
hcp-Co has only one easy-axis [00.1] for magnetization, whereas
fcc-Co has four easy axis of [111]. The energy of
magnetocrystalline anisotropy of hcp-Co is higher than fcc-Co
[Centre d'information du cobalt, Cobalt monograph, Brussels,
Belgium, (1960), pp 95-100]. The Curie temperature of hcp-Co is
887.degree. C. and fcc-Co is 1121.degree. C.
[0501] XRD results of deposits obtained at various solution pHs
and. CDs are shown in FIG. 79 and FIG. 80 (25.degree. C.), and FIG.
81 to FIG. 84 (60.degree. C.). These results are summarized in
Table 24. Most deposits obtained at 25.degree. C. (10 and 50
mA/cm.sup.2) were non-crystalline except for pH 2 at 10 mA/cm.sup.2
containing (10.0) and (00.2) peaks of a-Co. Decreased solution pH
did not eliminate Sm(OH).sub.3; (11.0) peaks of Sm(OH).sub.3 were
found in deposits at 25.degree. C. between pH 2 and 6. On the other
hand, the Sm(OH).sub.3 peak was not observed at 60.degree. C. At
60.degree. C. for different pHs, the change in orientation with
increasing CDs were similar.
TABLE-US-00024 TABLE 24 Dependence of XRD patterns on Sm deposit
content at various CDs and solution pH Solu- T tion Deposit Current
Density (mA/cm.sup.2) (.degree. C.) pH Properties 10 50 100 300 25
6 hcp peaks non-crystalline non-metallic Sm (at %) 2.3 7.4 5 hcp
peaks non-crystalline non-metallic Sm (at %) 1.7 7.0 4 hcp peaks
non-crystalline non-metallic Sm (at %) 1.7 3.1 3 hcp peaks
non-crystalline non-metallic Sm (at %) 0.7 2.7 2 hcp peaks (00.2) m
non- non-metallic (10.0) m crystalline Sm (at %) 0.5 1.5 60 6 hcp
peaks (00.2) m (10.1) w (10.1) w (10.0) w (10.1) w (11.0) w (11.0)
w (11.0) m (10.0) m (10.0) m (10.0) m Sm (at %) 2.3 7.4 9.2 16.7 5
hcp peaks (00.2) m (11.0) w (10.1) w non- (10.1) m (10.0) m (11.0)
w crystalline (11.0) m (10.0) w (10.0) s Sm (at %) 1.7 7.0 11.8
22.6 4 hcp peaks (00.2) w (00.2) w (10.0) w non- (10.1) w (10.1) w
crystalline (11.0) w (11.0) w (10.0) m (10.0) m Sm (at %) 1.7 3.1
10.8 28.1 3 hcp peaks (00.2) w (00.2) m (10.0) w (10.0) w (10.1) w
(10.1) w (11.0) w (11.0) m (10.0) m (10.0) m Sm (at %) 0.7 2.7 8.5
24.2 2 hcp peaks (00.2) m (00.2) w (00.2) w non- (10.1) m (10.1) w
(10.1) w crystalline (11.0) s (11.0) m (11.0) w (10.0) s (10.0) m
(10.0) w Sm (at %) 0.5 1.5 0.9 18.9 weak Sm(OH).sub.3 (10~50
mA/cm.sup.2 at 25.degree. C.), Sm.sub.2Co.sub.17 and SmCo.sub.3 (2
mA/cm.sup.2 at 60.degree. C.) peaks were not included s, m and w
compared the intensity of peaks, "s" = strong, "m" = medium, "w" =
weak non-crystalline defined as no .alpha.-Co peaks was found in
XRD
[0502] Generally, the .alpha.-Co (hcp) phase is stable at
temperature below 417.degree. C., and the {tilde over
(.beta.)}Co(fcc) phase is thermodynamically stable only above
417.degree. C. However, it was reported that both phases can be
obtained in electrodeposited Co with .alpha.-Co obtained at pH
higher than 2.9 and .beta.-Co at pH less than 2.4. (bath: Co
sulfate, NaCl, 18.degree. C., 12 mA/cm.sup.2) [J. Goddard and J. G.
Wright, Brit. J. Appl. Phys., 15, 807, (1964)]. Nakahara et al. [S.
Nakahara and S. Mahajan, Electrochem. Soc., 127, 283, (1980)]
(bath: Co sulfate, NaCl and boric acid, 25.degree. C., 10
mA/cm.sup.2) further proposed that the formation of metastable Co
hydride at low pH could be the reason for the formation of
.beta.-Co. High density inclusions of Co(OH).sub.2 were observed in
high pH (.about.5.7) deposits [S. Nakahara and S. Mahajan,
Electrochem. Soc., 127, 283, (1980)]. It was concluded that the
solution pH is the most important parameter governing the crystal
structure of electrodeposited Co where deposits at high pH results
in .alpha.-Co and low pH generates .beta.-Co [S. Nakahara and S.
Mahajan, Electrochem. Soc., 127, 283, (1980)].
[0503] For Co--Sm deposits from bath 1, .beta.-Co crystallites were
not found from solution pH from 6 to 2 at 10 & 50 mA/cm.sup.2
and 25.degree. C. (FIG. 79 and FIG. 80), and at 10-300 mA/cm.sup.2
and 60.degree. C. (FIG. 81 to FIG. 84)). Furthermore, inclusions of
Co(OH).sub.2 was not observed even for deposits obtained at pH 6.
In Hull Cell studies, it was observed that in the absence of
glycine, Co(OH).sub.2 and Sm.sub.2O.sub.3.CoO mixtures were found
in deposits. It has been reported that the Co-glycine complex can
inhibit the formation of Co(OH).sub.2 [C. F. Diven, F. Wang, A. M.
Abukhdeir, W. Salah, B. T. Layden, C. F. Geraldes, and D. M.
Freitas, Inorg. Chem., 42, 2774, (2003)]. The appearance of glycine
probably prevents inclusions of Co(OH).sub.2 by complexing with Co
ions.
[0504] p. Morphologies and Microstructures
[0505] SEM pictures of deposits obtained at various solution pHs
and CDs at 25.degree. C. and 60.degree. C. are shown in FIG. 65 and
FIG. 66 and FIG. 67 and FIG. 590, respectively. Dependence of
particle size on Sm deposit content at various pHs, temperatures
and CDs is shown in FIG. 59.
[0506] At 25.degree. C. (FIG. 85), there were more microcracks in
deposits obtained at higher CDs or solution pHs. These changes
resulted in high Sm deposit contents. At 60.degree. C. (FIG. 87),
microcracks were less significant compared to 25.degree. C. even
for high Sm deposit contents. For electrodeposited Co-rich Co--Sm
alloys (before the formation of intermetallic compounds) the
addition of Sm into the Co matrix probably induced internal stress
by the misfit of lattice constants of Co and Sm. Further addition
of Sm increased internal stress increasing microcracks in the
deposits. Stacking faults and defects formed during the
electrodeposition also resulted in internal stress. Elevated
solution temperatures resulted in adsorbed atoms of higher mobility
on the cathode surface facilitating their reaching kink or terrace
sites that reduce defects and internal stress in deposits.
[0507] High magnitude (50,000.times.) SEM results at 25.degree. C.
show ridge-shaped microstructures were observed at pH 2 below
Sm=3.1 at % (FIGS. 86(g) & (h)). Ridge-shaped microstructures
were also observed in Co-rich Co-Fe.sup.28 and Ni--Co.sup.29
alloys. At pH 4 and 10 mA/cm.sup.2, tiny roundish particles mixed
with large plate-shaped particles resulted in a wider distribution
of particle size (FIG. 86(d)).
[0508] At 60.degree. C., microstructures at pH 2 were more compact
(FIGS. 88(g) & (h)). At 50 mA/cm microstructures were large
ridge-shaped (FIG. 88(h)). With decreased CD to 10 mA/cm.sup.2,
tiny protrusions embedded in the ridge-shaped matrix had a
two-phase structure (FIG. 88(g)). For deposits with similar Sm
deposit contents obtained at different pH baths could have quite
different microstructure shapes and particle sizes (for example,
FIG. 88(d) vs. (h), FIG. 86(a) vs. (i)).
[0509] Vicenzo and Cavallotti studied the growth modes of
electrodeposited Co from sulfamate baths. Different pH baths led to
different morphologies and microstructures. Three basic modes were
identified as: outgrowth, lateral growth and cluster growth which
were strongly dependent on solution pH. Increased particle size was
found as decreased [A. Vicenzo, P. L. Cavallotti. Electrochim.
Acta, 49, 4079, (2004)]. In Co--Sm electrodeposition, deposit
microctructure varied with solution pH. However, the dependence of
particle size on solution pH was not significant.
[0510] At a fixed solution pH, increased CD or decreased solution
temperature generally brought about an increase in Sm deposit
content leading to the reduction of particle size (FIG. 89).
However, at pH 2 and 60.degree. C. particle size increased by
increasing CD from 10 to 50 mA/cm.sup.2 (FIG. 88). The dependence
of particle size at various pH on Sm deposit content was more
scattered compared to a fixed pH (pH6, FIG. 74). Different shapes
of microstructures obtained at different pH make this dependence
more complex.
[0511] q. Magnetic Properties
[0512] FIG. 90 gives magnetic properties of deposits obtained at
25, 60.degree. C. and at various solution pHs. Ms values were
dependent on alloy compositions but not on solution pH. Ms
decreased with increased Sm deposit content and were in good
agreement with sputtered deposits.
[0513] Similar to the results on the effect of CD and solution
temperatures in FIG. 18(c), Hc.sub..parallel. decreased with
increased Sm deposit content (FIGS. 90(c) & (d)) due to
decreased (FIG. 89). Hc.sub..parallel. varied little with Sm
deposit content (FIGS. 90(c) & (d)) for small change in
.sigma..sub..parallel. with increased Sm content (FIG. 89) (see
FIG. 77).
[0514] In-plane squareness was higher than perpendicular due to the
alignment of magnetization direction along the in-plane direction
to reduce the demagnetization energy. Squareness decreased with
increased Sm content by the change from crystalline to
noncrystalline structure.
[0515] r. Effect of Fluid Dynamics
[0516] Alloy Composition: The rotating disk electrode (RDE), which
changes the mass transfer rate of electrolyte from the bulk
solution to the cathode surface by varying the rotation rate, was
used to study the effect of fluid dynamics on Co--Sm alloy
deposition. Because the brass substrate was placed facing down to
the button of the cell, when the RDE was stationary, hydrogen
bubbles generated from water reduction accumulated on the cathode
surface resulting in burnt deposits with poor adhesion (films fell
off the electrode after electrodeposition). For this reason,
deposits obtained from parallel electrodes (without agitation) were
used in place of 0 rpm (deposits) in the following discussions to
assess the difference with/without agitation.
[0517] Deposit Sm content sharply decreased, then reached a
constant by increase in rotating rate (FIG. 91(a)). On the other
hand, CE increased with increasing rotating rate (FIG. 91(b)).
Agitation by RDE resulted in metallic deposits at 100 mA/cm.sup.2
in contrast to deposits obtained without agitation (parallel
electrodes), but higher Sm deposit content were not obtained. Even
though the concentration of Co ions (0.05M) was much lower than Sm
ions (1M) in bath 1, the deposition rate of Co was much greater
than Sm (FIG. 92). A higher rotating rate did not significantly
increase the deposition rate of Sm; but enhanced substantially the
deposition of Co and suppressed H.sub.2 gas evolution. This
indicates that the decrease in Sm deposit content by a greater
agitation rate (FIG. 91(a)) was due to the increase in Co
deposition rate (Sm deposition rate remained unchanged). These
results indicate mass transfer effects in the co-deposition of
Co.
[0518] As discussed in the previous section on parallel
electrodes,, the deposits were not metallic at 100mA/cm.sup.2.
White powder and burnt regions appeared on deposit surfaces. These
non-metallic regions were confirmed as mixtures of oxides and
hydroxides in the Hull cell study. SEM pictures of the deposit at
100 mA/cm.sup.2 (parallel electrodes, no agitation) are shown in
FIGS. 93(a)-(c). High density microcracks were found in the deposit
(FIG. 93(a)) and the white powder had a porous microstructure (FIG.
93(c)). For deposits obtained with agitation (1000 and 2000 rpm),
metallic deposits were obtained and microcrack densities remained
the same (comparing FIGS. 35(a), (d) & (e)) but the porous
microstructure disappeared.
[0519] s. Magnetic Properties
[0520] The morphology and microstructure of the non-metallic
deposit (confirmed as mixtures of hydroxides and oxides) obtained
at 100 mA/m.sup.2 by parallel electrodes was compared to metallic
deposits in the previous section. The appearance of oxide and
hydroxide phases in this deposit also caused the degradation of
magnetic properties, such as Ms. Compared to to sputtered Co--Sm
alloys with similar Sm content, this deposit (parallel electrodes,
25.degree. C., no agitation, 100 mA/cm, bath 1) had much lower Ms
(about 30% f sputtered) (FIG. 94(a)).
[0521] Similar to the results of magnetic properties discussed in
previous sections, Hc and squareness of deposits showed strong
dependence on Sm deposit content. Perpendicular He decreased
significantly but in-plane Hc decreased little by increasing Sm
deposit content. In addition, Hc was higher in the perpendicular
direction. In-plane squareness was higher than perpendicular
squareness; squareness decreased more in in-plane direction than in
the perpendicular direction with decreased Sm deposit content.
[0522] t. Effect of Sm Sulfamate
[0523] Alloy Composition: Baths containing 0.05M Co sulfate, 0.15M
glycine and Sm sulfamate varying from 0.25 to 1M were used to study
the effect of Sm sulfamate on deposit properties. The decrease of
Sm sulfamate concentration resulted in non-metallic deposits (Table
25). White powders consisting of Sm(OH).sub.3 and Co(OH).sub.2
(XRD) appeared in deposits obtained for Sm sulfamate concentration
<1M at 60.degree. C. and low CDs (25 & 50 mA/cm.sup.2).
CD.sub.max (the highest CD with metallic deposits) decreased as Sm
sulfamate concentration decreased (Table 25).
[0524] In general, decreased Sm sulfamate concentration increased
Sm deposit content (FIG. 95(a)). CE increased with decreased Sm
sulfamate concentration (FIG. 95(b)). The deposition rate of Sm and
Co was enhanced by decrease in Sm sulfamate concentration, whereas
Hi evolution was suppressed (FIG. 96). However, by decrease in Sm
sulfamate concentrations, Sm(OH).sub.3 or Sm oxide was found in
metallic appearing deposits (Table 25) at 25.degree. C. (FIG. 97
& FIG. 98) and 60.degree. C. (FIG. 99 & FIG. 100). The
precipitation of Sm(OH).sub.3 or Sm oxide in deposits may
contribute to the increase in Sm deposit content with decreased Sm
sulfamate concentrations.
TABLE-US-00025 TABLE 25 Deposit appearance obtained at various Sm
sulfamate concentrations, CDs and temperatures [Sm sulfamate] 1M
0.75M 0.5M 0.25M 25.degree. C. CD (mA/cm2) 25 M M M M 50 M M M b
100 b b b B 60.degree. C. CD (mA/cm2) 25 M w w w 50 M m w w 100 M M
M b 300 M M b B 500 M b B B
[0525] u. Crystal Structures
[0526] XRD results in the previous section show weak (11.0) peaks
of Sm(OH).sub.3 in deposits obtained at 25.degree. C. (FIG. 67). At
25.degree. C. and 25 mA/cm.sup.2, similar XRD patterns were found
for deposits obtained from baths containing various Sm sulfamate
concentrations (FIG. 97). On the other hand, at 50 mA/cm.sup.2
(25.degree. C., FIG. 98), the intensity of Sm(OH).sub.3 (11.0)
peaks became stronger when Sm sulfamate concentrations were less
than 0.75M. Meanwhile, Co(OH).sub.2 (11.0) peaks appeared for Sm
sulfamate concentrations less than 0.5M.
[0527] At 60.degree. C., no hydroxide peaks were found in deposits
from bath 1 (Sm sulfamate=1M) (FIG. 68). However, Sm(OH).sub.3
(11.0) and Co(OH).sub.2 (11.0) peaks appeared for Sm sulfamate
concentrations of 0.75M (60.degree. C. and 50 mA/cm.sup.2) or less
with peak intensities increasing with decreasing Sm sulfamate
concentrations (FIG. 99). A (111) peak of SmO was observed when Sm
sulfamate concentration reached 0.25M. With further increase of CD
to 100 mA/cm.sup.2 (FIG. 100), peaks of CoO and SmCoO.sub.3 were
found.
[0528] Generally, decrease in Sm sulfamate concentrations resulted
in more hydroxides (Sm(OH).sub.3 and Co(OH).sub.2), except for
deposits obtained at 25.degree. C. and 25 mA/cm.sup.2. SmO, CoO and
SmCoO.sub.3 were observed at 60.degree. C. and 100 mA/cm.sup.2 for
Sm sulfamate concentrations of 0.5M and less. Co(OH).sub.2 and CoO
were not only found in non-metallic deposits but also in metallic
deposits (FIG. 98(b), FIG. 99(c) and FIG. 100(b)) degrading their
saturation magnitization.
[0529] v. Magnetic Properties
[0530] Magnetic properties of deposits obtained at various Sm
sulfamate concentrations are shown in FIG. 101. Ms values of
non-metallic deposits were 1/5 to 1/4 that of sputtered deposits.
Co(011)7 or CoO in these non-metallic deposits (FIG. 40(a) and FIG.
42(a)) degraded Ms by reducing the ferromagnetic phase (metallic
Co) to non-ferromagnetic phases (Co(OH).sub.2 or CoO). For metallic
deposits containing Co(OH).sub.2 or CoO obtained at 25.degree. C.,
50 mA/cm.sup.2, [Sm sulfamate]=0.5M (FIG. 40(b)) and at 60.degree.
C., 100 mA/cm.sup.2, [Sm sulfamate]=0.5M (FIG. 42(b)), Ms values
were also much lower than sputtered deposits.
[0531] Similar to previous observations (FIG. 76(c)), He depended
on Sm deposit content. Higher Sm deposit content resulted in lower
Hc (compare FIG. 101(e) with (a), (f) with (b)); the change in
perpendicular Hc was more significant than in-plane Hc.
[0532] Squareness followed similar trends as discussed (FIG.
76(d)): in-plane squareness was higher than perpendicular, and
squareness decreased with increased Sm deposit content (compare
FIG. 101(g) with (a), (h) with (b)).
[0533] w. Effect of Glycine
[0534] Alloy Composition: Baths consisting of 1M Sm sulfamate,
0.05M Co sulfate and glycine varied from 0.05 to 0,5M were used to
study the effect of glycine on deposit properties. Dependence of Sm
content and current efficiency on glycine is in FIG. 102.
[0535] At 25.degree. C., low glycine concentrations resulted in
non-metallic deposits. Metallic deposits were obtained when glycine
concentration was higher than 0.1M at 25 mA/cm.sup.2 and 0.15 M at
50 mA/cm.sup.2. For metallic deposits obtained at 25.degree. C., Sm
deposit content decreased with increasing glycine concentration. At
60.degree. C. and low CDs (25 and 50 mA/cm.sup.2), Sm deposit
content increased, reached a maximum and then decreased with
glycine increased from 0 to 0.5M; highest Sm contents were obtained
at 0.15M glycine. With further increase in CD to 300 mA/cm.sup.2,
the highest Sm content was obtained at 0.1M glycine, and metallic
deposits were not observed at glycine concentration below 0.1M.
Highest Sm contents were obtained at glycine concentration between
0.1M (glycine: Co.sup.2+=2:1) and 0.15M (glycine: Co.sup.2+=3:1).
CE increased with increased glycine concentration at 25.degree. C.,
whereas had no significant dependence on glycine concentration at
60.degree. C.
[0536] According to the mechanism proposed by Schwartz et al [M.
Schwartz, N. V. Myung, and K. Nobe, J. Electrochem. Soc., 151,
C468, (2004)], a heterodinuclear complex containing Sm and Co ions
and glycine resulted in the co-deposition of Sm with Co. Different
glycine to metal ions ratio may change the complex composition
(i.e. types and concentrations) in solutions affecting the
reduction of Sm and Co and resulting in different Sm deposit
contents.
[0537] x. Crystal Structure and Microstructure
[0538] Addition of glycine prevents the precipitation of
Co(OH).sub.2 and Sm(OH).sub.3 as shown in the Hull cell results.
Formation of Co-glycine complex has been reported to inhibit the
formation of Co(OH).sub.2 in aqueous solutions.sup.31 and could be
the reason of preventing the precipitation of hydroxides in
deposits. More studies by parallel electrode deposition will be
discussed in this section. At 25.degree. C. weak Sm(OH).sub.3
(11.0) peaks were found in deposits were found in deposits obtained
from 0.15M glycine solutions (FIG. 103(b) or FIG. 67). However, at
60.degree. C. 0.15M glycine effectively prevented the precipitation
of hydroxides in deposits (FIG. 104(b)).
[0539] On the other hand, deposits obtained at 0.05M and 0.5M
glycine concentrations had stronger Sm(OH).sub.3 (11.0) peaks
compared to 0,15M glycine (25.degree. C.: FIG. 103, 60.degree. C.:
FIG. 104). Co(OH).sub.2 (11.0) peaks were also found in these
deposits (0.05 and 0.5M glycine). Adding too little (glycine:
Co.sup.2+=1:1) or too much glycine (glycine: Co.sup.2+=10:1) to the
solution did not prevent the formation of hydroxides (Co(OH).sub.2
and Sm(OH).sub.3).
[0540] y. Magnetic Properties
[0541] FIG. 105 shows the magnetic properties of deposits obtained
at various glycine concentrations. For metallic deposits obtained
from the solutions of glycine concentrations ranging from 0.05 to
0.5M had Ms values comparable to sputtered deposits (FIGS. 105(c)
& (d)). Even in the presence of some hydroxides in deposits
obtained at 0.05M and 0.5M glycine (FIG. 103 and FIG. 104),
significant degradation of Ms values were not observed compared to
the deposits containing hydroxides and oxides obtained at low Sm
sulfamate concentrations (see FIG. 101).
[0542] In-plane and perpendicular He for deposits obtained by
varying glycine concentrations did not change significantly (FIGS.
105(e)&(0), but perpendicular was greater than in-plane Hc. At
25 and 60.degree. C., in-plane squareness was greater than
perpendicular squareness.
[0543] z. Effect of NH.sub.4 Sulfamate
[0544] Alloy Composition: Schwartz et al [M. Schwartz, N. V. Myung,
and K. Nobe, J. Electrochem. Soc., 151, C468, (2004)] studied the
electrodeposition of Co--Sm alloys under agitation of the plating
solution containing 0.9M Sm sulfamate, 0.12M Co sulfamate, 0.36M
glycine and 0.9M NH.sub.4 sulfamate resulting in maximum Sm
deposits of 8 at %. However, Hull cell results indicated that the
presence of NH.sub.4 sulfamate in solution reduced Sm deposit
content. In the absence of NH.sub.4 sulfamate (bath 1), a Sm
deposit content of 26 at % was obtained at 60.degree. C. and 650
mA/cm.sup.2 from an unagitated solution. A Sm deposit content of 32
at % was obtained with parallel electrodes from bath 1 at
60.degree. C. and 500 mA/cm.sup.2 (unstirred).
[0545] Although addition of NH.sub.4 sulfamate resulted in
decreased Sm content, it was of interest to study how NH.sub.4
sulfamate reduced Sm deposit content and affected deposit
properties. Baths consisting of 1M Sm sulfamate, 0.05M Co sulfate,
0.15M glycine and NH.sub.4 sulfamate varied from 0 to 1M were used
to study the effect of NH.sub.4 sulfamate. Addition of NH.sub.4
sulfamate resulted in decreased Sm content (FIG. 48(a)) confirming
the Hull cell results. The decrease in Sm content was more
substantial at higher CDs. CE increased with increased NH.sub.4
sulfamate concentration at 25.degree. C. but varied little at
60.degree. C. (FIG. 106(b)). Increased NH.sub.4 sulfamate
concentration suppressed Sm deposition (FIG. 107(a)) and enhanced
Co deposition (FIG. 107(b)) leading to decreased Sm content (FIG.
106(a)).
[0546] The heterodinuclear complex containing Sm and Co ions and
glycine was proposed resulting in the co-deposition of Sm with Co
[M. Schwartz, N. V. Myung, and K. Nobe, J. Electrochem. Soc., 151,
C468, (2004)]. However, NH.sub.3 from the deprotonated
NH.sub.4.sup.+ could compete with glycine to form other complexes
with Co and Sm ions and result in changes in compositions of
complexes in solution. This can decrease Sm deposit content by
suppressing co-deposition of Sm.
[0547] aa. Crystal Structure
[0548] FIG. 108 and FIG. 51 compared the crystal structures of
deposits obtained from solution with (bath 1)/without 1M NH.sub.4
sulfamate (bath 8) at 25 and 60.degree. C., respectively.
[0549] At 25.degree. C., non-crystalline deposits were obtained at
CD over 10 mA/cm.sup.2 for both baths with/without 1M NH.sub.4
sulfamate. At 2 mA/cm.sup.2, only the .alpha.-Co (00.2) peak was
found in the presence of 1M NH.sub.4 sulfamate (bath 8). In its
absence (bath 1), addition of .alpha.-Co (10.1), (11.0) and (10.0),
SmCo.sub.5 (hexagonal) (20.1) and Sm.sub.2Co.sub.17 (hexagonal)
(20.2) peaks were observed. It was interesting to note the absence
of the Sm(OH).sub.3 peak in deposits from bath 8 for CD.gtoreq.25
mA/cm.sup.2. At 60.degree. C. (FIG. 109), the dependence of crystal
structure on CD for deposits from bath 8 was similar to bath 1,
except no (10.1) peak was observed. Furthermore, unlike deposits
obtained at 25.degree. C., 60.degree. C. deposits did not exhibit
the Sm(OH).sub.3 peak.
[0550] bb. Morphologies and Microstructures
[0551] For deposits obtained at the same temperature and current
density the presence of NH.sub.4 sulfamate resulted in much smaller
microcracks in deposits than in its absence (FIG. 110). The former
produced lower Sm deposit content leading to lower internal
stressed deposits as discussed in the previous section.
[0552] Microstructures obtained from baths with/without 1M NH.sub.4
sulfamate were quite similar, except at 60.degree. C. and 50
mA/cm.sup.2 (FIG. 111).
[0553] At 60.degree. C. and 50 mA/cm.sup.2, rigid-shaped rods and
spherical particles were observed in deposits obtained from bath 8
(with 1M NH.sub.4 sulfamate) (FIG. 111(b)). These microstructures
were more compact compared to deposits from bath 1 (without
NH.sub.4 sulfamate).
[0554] cc. Magnetic Properties
[0555] FIG. 112 shows the magnetic properties of deposits obtained
from baths containing various NH.sub.4 sulfamate concentrations.
Deposits obtained from solutions with/without NH.sub.4 sulfamate
had similar Ms and were in accord with the Ms of sputtered deposits
(FIGS. 112(a) & (b)). For the deposits (with NH.sub.4
sulfamate), Hc.perp. was much greater than Hc.sub..parallel. and
decreased significantly by increasing Sm deposit content, whereas
Hc.sub..parallel. varied little (FIGS. 112(c) & (d)). Both
in-plane and perpendicular squareness decreased with increase in Sm
content and the former significantly larger. The dependence of He
and squareness on Sm content was not affected by the presence of
NH.sub.4 sulfamate.
[0556] dd. Supporting Electrolytes
[0557] Alloy Composition: Addition of NH.sub.4 sulfamate in
solution was found to suppress the deposition of Sm and enhance the
deposition of Co resulting in decreased Sm content. As a supporting
electrolyte, NH.sub.4 sulfamate could change or modify the
glycinato-complex structure in solution thereby affecting the
deposition of Sm and Co.
[0558] Taube and Gould [H. Taube and E. S. Gould, Acc. Chem. Res.,
2, 321, (1969)] indicated that NH.sub.3 is not a good bridging
ligand for electron transfer in redox reactions, and a metal
ion-NH.sub.3 complex could result in low reaction rates. Further,
inclusion of Cl-- ions could accelerate redox reactions and is
referred as a good bridging ligand or mediating group. Therefore,
it was of interest to include the effect of bridging ligands on
electrodeposition of Co--Sm alloys. Supporting electrolytes of 1M
NH.sub.4 sulfamate, NH.sub.4Cl or KCl were added to bath 1 to study
the influence of NH.sub.3 and Cl-- bridging ligands on deposit
composition and properties.
[0559] The highest Sm content of metallic deposits obtained from
these baths ranked as: 1M KCl (18 at % at 50 mA/cm.sup.2) >no
supporting electrolyte (14.5 at % at 50 mA/cm.sup.2)>1M
NH.sub.4Cl (9.7 at % at 100 mA/cm.sup.2)>1M NH.sub.4 sulfamate
(8.1 at % at 300 mA/cm.sup.2) from 25.degree. C. solutions (FIG.
113(a)). Sm deposit content increased with the addition of Cl-- and
decreased with the addition of NH.sub.4.sup.+ (or NH.sub.3).
Addition of KCl did not increase CD.sub.max. Compared to no
supporting electrolyte (50 mA/cm.sup.2), however, the addition of
NH.sub.4Cl and NH.sub.4 sulfamate resulted in increased CD.sub.max
to 100 and 300 mA/cm.sup.2, respectively.
[0560] With increased solution temperatures (60.degree. C.),
addition of NH.sub.4Cl or NH.sub.4 sulfamate both extended the
CD.sub.max to 900 mA/cm.sup.2, whereas addition of KCl limited the
CD.sub.max to 300 mA/cm.sup.2 (FIG. 113(b)). The highest Sm deposit
contents were: no supporting electrolyte (32 at % at 500
mA/cm.sup.2)>NH.sub.4Cl (27 at % at 900 mA/cm.sup.2) NH.sub.4
sulfamate (27 at % at 900 mA/cm.sup.2)>KCl (21 at % at 300
mA/cm.sup.2). Because of the lower limiting CD.sub.max (300
mA/cm.sup.2), the highest Sm deposit content from the
KCl-containing bath was not higher than deposits from NH.sub.4Cl or
NH.sub.4 sulfamate baths. However, with CDs<300 mA/cm.sup.2, the
Sm deposit content ranked: KCl>no supporting electrolyte
NH.sub.4Cl>NH.sub.4 sulfamate, similar to the deposits from
25.degree. C. baths. The dependence of Sm content on NH.sub.4.sup.+
and Cl-- ions (as bridging ligands) was observed; at a fixed CD,
the Sm contents obtained from Cl-- containing solutions were higher
than NH.sub.4-containing solutions. CEs decreased with increasing
CD at 25.degree. C.; CDs at 60.degree. C. decreased but reached a
minimum at 300 mA/cm.sup.2 and then increased slightly (FIG.
114).
[0561] At 25.degree. C., Sm deposit content increased with
increasing CD (FIG. 113(a)) mainly due to the decreased. Co
deposition (FIG. 115(a)); the decrease of Co deposition was sharper
for solutions in the absence of supporting electrolyte. At
60.degree. C., increasing CD increased Sm deposition and decreased
Co deposition (FIG. 115(b)). At both 25 and 60.degree. C., Sm
deposition was enhanced by addition of Cl-- ions and suppressed by
addition of NH.sub.4.sup.+ ions (FIGS. 115(c) & (d)).
[0562] ee. Morphologies and Microstructures
[0563] FIG. 116 and FIG. 117 show the SEM of deposit surface
obtained from baths at temperature of 25 (at 25 mA/cm.sup.2) and
60.degree. C. (at 300 mA/cm.sup.2), respectively. The morphology of
deposits shows little effect of the supporting electrolyte.
[0564] ff. Magnetic Properties
[0565] FIG. 118 shows the magnetic properties of deposits obtained
from solutions with/without supporting electrolytes.
[0566] Addition of NH.sub.4 sulfamate, NH.sub.4Cl or KCl did not
degrade deposit magnetic saturation (Ms). These Ms values were
close to sputtered deposits (FIGS. 118(a) & (b)). While
Hc.perp. decreased sharply and Hc.sub..parallel. varied little with
increased Sm content, the addition of various supporting
electrolytes had little effect on deposit coercivity (FIGS. 118(c)
& (d)). Both in-plane and perpendicular squareness (Mr/Ms)
decreased with the former significantly higher than the latter.
Addition of supporting electrolyte containing Cl--, especially KCl,
resulted in higher in-plane squareness compared to deposits from
other solutions at D60.degree. C. (FIG. 118(1)).
[0567] 6. Aqueous Electrodeposition of Magentic Co--Sm
Alloys--Pulse Current (PC) Electrodeposition Studies
[0568] In pulse current (PC) electrodeposition studies, an
interrupted cathodic current with square waveform is applied for a
specific time period (T.sub.on) and then returned to ground zero
for another specific time period (T.sub.off); such a pulse period
consisting of T.sub.on and T.sub.off repeats during the
electrodeposition. Three important features in PC electrodeposition
are: peak current density (PCD), concentration relaxation of
reactants and kinetic selected deposition [Ibl, J. C. Puippe and H.
Angerer, Surf Tech., 6, 287, (1978); N. Ibl, Surf Tech., 10, 81,
(1980).]. These characteristics of PC electrodeposition affect
alloy compositions and crystal properties of deposits.
[0569] Pulse current results in a very high instantaneous peak
current density and hence a very negative cathodic potential.
Higher CDs or more negative cathodic potentials have been shown to
increase Sm deposit content in DC electrodeposition studies. Hull
cell studies also show this trend in PC electrodeposition.
Therefore, PC electrodeposition of high peak current densities can
increase Sm deposit content. In addition, a very negative cathodic
potential also increases the nucleation rate and can change the
particle size and microstructures of deposits.
[0570] Short T.sub.on and longer T.sub.off provides more relaxation
of the reactant (metal ions or complexes) concentrations at the
cathode surface preventing the depletion of reactants and
minimizing mass transfer effects. This changes the alloy
composition. OH-- ions were generated only during T.sub.on in PC
electrodeposition (DC generates OH-- ions continuously during
electrodeposition.). This can prevent unwanted Sm and Co
hydroxides/oxides in deposits.
[0571] Frequency of pulse current also change alloy compositions.
Unlike DC obtaining deposits steadily during electrodeposition, PC
enables the kinetic selected deposition by increased frequency. In
alloy electrodeposition, higher frequency increases deposit content
of metal with higher reduction rates.
[0572] Disclosed herein is how PC electrodeposition parameters
affected alloy properties (i.e., composition, crystal and magnetic
properties), and correlate deposit magnetic behavior to other alloy
properties. In addition, deposits obtained by DC and PC
electrodeposition are compared.
[0573] The main goals of PC electrodeposition include: Obtaining
high Sm deposit content of Co--Sm alloys; Determining the
dependence of the deposit properties of Co--Sm alloys on PC
electrodeposition parameters; Studying the relation between the
deposit magnetic properties and PC electrodeposition parameters;
Comparing deposit properties obtained by DC and PC
electrodeposition.
[0574] FIG. 120 shows the experimental flowchart of a PC experiment
which mainly includes four parts: pretreatment of cathode, PC
electrodeposition, post-treatment of specimen and characterization.
Definitions, setup and design of PC electrodeposition, pretreatment
and post-treatment, and the characterization and analysis of the
specimens will be detailed in following sections.
[0575] a. Definitions and Parameters of PC Electrodeposition
[0576] PCD (peak current density) is the maximum CD in one complete
pulse cycle. T.sub.on, is the time duration of the on-current in
one complete pulse cycle. T.sub.off is the time duration of the
off-current in one complete pulse cycle. Period is the total time
duration in one complete pulse cycle,
period=T.sub.total=T.sub.on+T.sub.off. Frequency is defined as the
number of complete cycles per second,
f = 1 period = 1 T on + T off . ##EQU00013##
Duty cycle (y) is defined as the ratio of Ton to period,
.gamma. = T on T on + T off = T on f . ##EQU00014##
PCD.sub.max is defined as the highest PCD to obtain metallic
appearing deposits.
[0577] b. Setup of PC Electrodeposition
[0578] FIG. 122 shows the setup of the PC electrodeposition system.
A Kraft Dynatronixpower generator (model DRP 20-5-10) served as the
power source for PC electrodeposition. A coulometer was used to
measure the charge passed during electrodeposition. The deposits
were obtained in a 250 ml beaker filled with the plating bath of
240 ml. Brass panels (2.times.1.9 cm) served as cathodes and a
platinum sheet (3.times.36 cm) was used as the anode; the distance
between the cathode and the anode is 4 cm. A shielding panel with a
2.times.2 cm opening window, designed by the simulation result of
ANSYS (a finite element analysis software), was placed between the
cathode and anode to provide a uniform current density distribution
on cathode to minimize the thickness variation of the deposit.
[0579] C. Design of Experiments
[0580] In this study, operating conditions for PC
electrodeposition, such as peak current density, solution
temperature, duty cycle, frequency and T.sub.on will be varied.
Various peak current densities (100-1200 mA/cm.sup.2), bath
temperatures (25-60.degree. C.), duty cycle (0.001-0.3), frequency
(10-2 k Hz), and To.sub.n (0.05-2 ms) were used to obtain deposits.
Bath 1 (1M samarium sulfamate, 0.05M cobalt sulfate, 0.15M glycine)
was used to determine the key variables in the PC
co-electrodeposition of Co--Sm alloys.
[0581] d. Pretreatment and Post-Treatment
[0582] Before electrodeposition, the brass panels were mechanically
cleaned, soaked in alkaline 0.1M NaOH solution for 10 min., rinsed
in deionized water, immersed in 10% HCl for 30 seconds and than
rinsed with deionized water. Unless otherwise noted, the total
charge passed was 50 coulombs; solutions were not agitated during
electrodeposition.
[0583] After the deposition of Co--Sm alloys for 50 coulombs, the
deposits were removed from plating solution, rinsed with deionized
water, and dried with nitrogen gas. Disk-shaped specimens of
diameter of 6.4 mm (specimen area=31.7 mm.sup.2) were die-punched
out from deposits for analysis.
[0584] e. Characterization and Analysis
[0585] The samarium
Sm Sm + Co ( at % ) ##EQU00015##
and cobalt deposit content
Co Sm + Co ( at % ) ##EQU00016##
were determined by an energy dispersive x-ray spectroscopy (EDS)
with a Kevex detector in a Cambridge SEM; the mass of deposited
cobalt was measured by a Perkin Elmer flame atomic absorption
spectroscopy (AA, mode 631); the crystal structure, orientation,
phase identification and grain size were determined by a
PANalytical x-ray diffraction system (XRD, model X'Pert Pro); the
surface morphology, microstructure and grain size were observed by
a JEOL scanning electron microscopy (SEM, model JSM-6700F);
magnetic properties were determined by a ADE Tech. vibrating sample
magnetometer (VSM, model 1660). Unless otherwise noted, the
experimental data presented are restricted to deposits with a
metallic appearance.
[0586] f. Effect of PCD and Solution Temperature
[0587] Alloy Composition: Bath 1 (1M Sm sulfamate, 0.05M Co
sulfate, 0.15M glycine) was used to study the effects of peak
current density (PCD) and solution temperature on alloy properties.
Ton was maintained constant as 0.1 ms and duty cycle y of 0.1. FIG.
123 compares the effect of PCD (or CD) and solution temperature on
Sm deposit content and current efficiency in PC and DC
electrodeposition. Similar to DC electrodeposition, increased PCD
resulted in increased Sm deposit content. At 25.degree. C., the
PCD.sub.max of 1050 mA/cm.sup.2 was much higher than the CD.sub.max
of 50 mA/cm.sup.2 resulting in a higher maximum. Sm deposit content
by PC (20.3 at %) than by DC (14.5 at %). On the other hand, at
60.degree. C. although the PCD.sub.max (2100 mA/cm.sup.2) was
higher than CD.sub.max (500 mA/cm.sup.2), maximum Sm content by PC
(11.6 at %) was lower than by DC (32.1 at %) due to smaller
Sm content PCD ( or CD ) ##EQU00017##
of PC electrodeposition. PC electrodeposition at 60.degree. C.
resulted in a lower maximum Sm content (11.6 at %) compared to
25.degree. C. (20.3 at %). On the other hand, DC electrodeposition
showed the opposite result of higher maximum Sm content at
60.degree. C. (32.1 at %) than 25.degree. C. (14.5 at %). This
confirms the Hull cell studies. Increased PCD led to decreased
current efficiency, and elevated solution temperatures resulted in
higher current efficiencies in PC electrodeposition.
[0588] At 60.degree. C., PC reduced Sm deposition and enhanced Co
deposition compared to DC electrodeposition (FIG. 124) resulting in
lower Sm contents in PC electrodeposition.
[0589] g. Crystal Structures
[0590] Compared to DC electrodeposition, Sm(OH).sub.3 was not found
in deposits by PC electrodeposition (FIG. 125). DC generates OH--
ions continuously during electrodeposition. On the other hand, OH--
ions were generated only during T.sub.on in PC electrodeposition.
Therefore, PC electrodeposition resulted in lower OH-- ion
concentration at the cathode surface and minimizing the folination
of Sm(OH).sub.3 at both 25 and 60.degree. C.
[0591] Deposits obtained at 25.degree. C. (FIG. 125, left) appeared
non-crystalline for PCD higher than 200 mA/cm.sup.2. Unlike DC
electrodeposition, non-crystalline deposits were not found in PC
electrodeposition at 60.degree. C. (FIG. 125, right). All deposits
obtained at 60.degree. C. were hcp crystallites, even up to 2100
mA/cm.sup.2. The changes in orientation with increased PCD (or Sm
content) were different than DC and not in agreement with
Pangarov's prediction [N. A. Pangarov, J. Electroanal. Chem., 9,
70, (1965).]. (00.2), (10.1), (11.0) and (10.0) peaks of hcp Co
were observed for deposits without following any role.
[0592] h. Morphology and Microstructures
[0593] FIG. 126 and FIG. 127 shows the SEM of deposits obtained at
25 and 60.degree. C., respectively. At 25.degree. C., increased PCD
resulted in increased Sm deposit content and decreased particle
size, similar to DC. Also, microstructures changed from
fiber-shaped nano-rods to roundish particles, and microcracks
increased with increased PCD.
[0594] However, for deposits obtained at 60.degree. C., particle
size decreased significantly by increased PCD from 100 to 300
mA/cm.sup.2 (FIGS. 127(c) & (f)) but changed little from 300 to
2100 mA/cm.sup.2 (FIGS. 127(f), (i) & (1)). Ridge-shaped
microstructures were observed in the deposits obtained at 100
mA/cm.sup.2 (60.degree. C.).
[0595] i. Magnetic Properties
[0596] FIG. 128 shows the hysteresis loops of deposits obtained at
various PCDs and solution temperatures. Similar to deposits by DC
electrodeposition, magnetization was easier in the in-plane
direction than the perpendicular direction indicating the easy-axis
(EA) along the in-plane direction and the hard axis (HA) along the
perpendicular direction. In-plane magnetization (M.sub..parallel.)
was higher than perpendicular magnetization (M.perp.). On the other
hand, Hc.perp. was higher than Hc.sub..parallel.. With increased
PCD deposits changed from anisotropic to isotropic magnetic
behavior at both 25 and 60.degree. C. Such a change was more
significant for deposits obtained at 60.degree. C. Ms and He
increased as solution temperature increased from 25 to 60.degree.
C.
[0597] Magnetic properties of deposits by DC and PC
electrodeposition are compared in FIG. 129. (Magnetization was more
complete in the in-plane than the perpendicular direction so that
Msii is used to represent Ms in the following discussion.) The
strong dependence of magnetic properties of deposits on Sm content
was similar to DC electrodeposition. PC Ms decreased linearly with
increased Sm deposit content, in agreement with sputtered films [H.
S. Cho, J. R. Salem, A. J. Kellock and R. B. Beyers, IEEE Trans.
Magnetics, 33, 2890, (1997).] (FIGS. 129(a) & (d)). Increased
Sm content caused decreased H.perp. but Hc.sub..parallel. varied
little (FIGS. 129 (b) & (e)). Hc.perp. declined and approached
Hc.sub..parallel. with increased Sm content. S.sub..parallel. was
higher than S.perp. confirming the aligning of the easy axis of
magnetization along the in-plane direction (FIGS. 129(c) &
(f)). Without wishing to be bound by theory, it is beleieved that
decreased S.sub..parallel. and S.perp. with increased Sm content
was due to the increased non-crystallinity of deposits.
[0598] j. Effect of Duty Cycle
[0599] Alloy Composition: Bath 1 was used to study the effects of
duty cycle on alloys properties with Ton=0.1 ms, PCD=200 or 500
mA/cm.sup.2. An increase in duty cycle (y) increased Sm content
linearly at 25.degree. C. and parabolically at 60.degree. C. (FIG.
130(a)). Increased Sm content was more significant at the lower
solution temperature (25.degree. C.) and higher PCD (500
mA/cm.sup.2). On the other hand, increased y resulted in
exponentially decreasing current efficiencies. The decrease was
more significant for deposit obtained at 25.degree. C. than at
60.degree. C.
[0600] Increased y did not enhance the deposition of Sm but
considerably suppressed the deposition of Co (FIG. 131) leading to
increased Sm deposit content (FIG. 130(a)). It was concluded from
the RDE experimental results that mass transfer effects were
greater for Co than Sm co-deposition. Increased y (decreased
T.sub.off) caused a lower Co concentration at the cathode surface
because less Co ions recovered from bulk solution for shorter
T.sub.off, resulting in the decrease of Co deposition.
[0601] k. Crystal Structures, Morphologies and Microstructures
[0602] Increased .gamma. resulted in increased Sm content and
changed deposits from crystalline to non-crystalline structures at
both 25 and 60.degree. C. (FIG. 132). Increased .gamma. also
induced more microcracks in deposits at both 25.degree. C. (FIGS.
133(a) & (d)) and 60.degree. C. (FIGS. 133(g), (j) & (m))
and led to decreased particle size at 25.degree. C. (FIGS. 133(c)
& (f)) and 60.degree. C. (FIGS. 133(i), (1) & (o)).
[0603] These deposit characteristics caused by increased Sm content
were also observed for DC electrodeposition. Increased Sm content
in the Co--Sm alloys could distort Co lattices probably changing
the deposits from crystalline to non-crystalline structures and
leading to more microcracks.
[0604] 1. Magnetic Properties
[0605] FIG. 134 shows the magnetic properties of deposits obtained
at various .gamma.. Similar to the previous observation (effect of
PCD and solution temperature on magnetic properties), magnetic
properties of deposits obtained at various .gamma. can be
correlated to their Sm content which controlled the crystal
structure and particle size. Ms values decreased with increased Sm
content. Ms obtained from various .gamma. (0.025-0.3) at both 25
and 60.degree. C. were in agreement with sputtered films [H. S.
Cho, J. R. Salem, A. J. Kellock and R. B. Beyers, IEEE Trans.
Magnetics, 33, 2890, (1997).]. Hc.perp. was higher than
Hc.sub..parallel.. Increased Sm content decreased Hc.perp. but
Hc.sub..parallel. varied little (FIGS. 134(b) & (e)). Hc.perp.
obtained at 25.degree. C. decreased linearly with increasing Sm
content, but at 60.degree. C. Hc.perp. decreased gradually for Sm
content less than 10 at % then dropped sharply. S.sub..parallel.
was higher than S.sub..parallel. Both S.perp. and S.perp. decreased
with increased Sm content (FIGS. 134(c) & (f)).
[0606] m. Effect of Frequency
[0607] Alloy Composition: Bath 1 was used to study the effect of
frequency. Duty cycle .gamma. was kept constant at 0.1, solution
temperature at 25.degree. C. and PCD at 100, 250 and 500
mA/cm.sup.2. Increased frequency resulted in linear decrease in Sm
deposit content (FIG. 135(a)).
[0608] Increased frequency enhanced Co deposition, especially at
low PCD, but Sm deposition varied little (FIG. 136) resulting in
decreased Sm deposit content. These results indicate that Co
deposition rate was greater than Sm deposition rate during
electrodeposition of Co--Sm alloys leading to decreased Sm content
at higher frequencies. Generally, increased frequency resulted in
increased current efficiency, except for the deposits obtained at
100 mA/cm.sup.2 and 2000 Hz.
[0609] n. Crystal Structures and Morphologies
[0610] With increased frequency, deposits obtained at 100
Am/cm.sup.2 and 25.degree. C. changed from non-crystalline to
crystalline (FIG. 137 left) probably due to decreased Sm content.
At low frequencies (100 Hz, 7.1 at % Sm), characteristic peaks for
crystallites were not found indicating non-crystalline deposits. At
medium frequencies (200-1 k Hz, 6.1-4.7 at % Sm), crystallites of
mixed (10.0) and (11.0) peaks were observed. At high frequencies (2
kHz, 1.7 at % Sm), there was a strong (00.2) peak. Deposits
obtained at 25.degree. C. and frequencies between 100 and 1 kHz had
similar morphologies (FIG. 137 right). Microcracks were present in
these deposits. However, for the deposits obtained at 100
mA/cm.sup.2 and high frequency of 2 kHz, about 30% of the surface
of the brass substrate was not covered by CoSm deposits (FIG.
137(d) right, FIGS. 138(a) & (b)). Increased PCD to 500
mA/cm.sup.2, the brass substrate was fully covered by deposits
(FIGS. 138(c) & (d)). In other words, low coverage of deposits
occurred only at high frequencies (2 kHz) and low PCD (100
mA/cm.sup.2).
[0611] o. Magnetic Properties
[0612] FIG. 139 shows the effect of frequency on magnetic
properties in PC electrodeposition (25.degree. C., .gamma.=0.1).
Similar to previous observations, magnetic properties of deposits
were dependent on the SM content.
[0613] Ms values decreased linearly with increased Sm content and
are in agreement with sputtered films [H. S. Cho, J.R. Salem, A. J.
Kellock and R. B. Beyers, IEEE Trans. Magnetics, 33, 2890, (1997).]
(FIG. 139(b)) in the frequency range between 100 and 2,000 Hz.
Increased Sm content decreased Hc.perp. but Hc.sub..parallel.
varied little (FIG. 139(c)). Although both S.sub..parallel. and
S.perp. decreased with increased Sm content (FIG. 134 (d)), the
decrease was less significant compared to the effect of PCD and
solution temperature (FIG. 129) and duty cycle (FIG. 134).
[0614] p. Effect of T.sub.on
[0615] Alloy Composition: Bath 1 was used to study the effects of
T.sub.on. Compared to studies discussed earlier, short T.sub.on
(0.1-2 ms) and long T.sub.off (98-99.9 ms) were investigated to
maintain the solution composition at cathode surface close to the
bulk composition upon initiation of each pulse. By doing this, not
only the effect of T.sub.on but also the deposition rates of Sm and
Co can be investigated. Pulse period (T.sub.on+T.sub.off) was fixed
at 100 ms, solution temperature at 25.degree. C. and PCD between
100 and 500 mA/cm.sup.2.
[0616] Increased T.sub.on resulted in a parabolic increase in Sm
content (FIG. 140(a)) at both 500 and 1000 mA/cm.sup.2. Metallic
deposits were obtained at T.sub.on below 2 and 1 ms for 500 and
1000 mA/cm.sup.2, respectively. Higher PCD reduced the maximum
T.sub.on for metallic deposits. The effects of T.sub.on on
individual Sm and Co deposition were quite different. Increased
T.sub.on led to a slightly higher Sm deposition rate (FIG. 141). On
the other hand, Co deposition increased, reached a maximum and
decreased with increased T.sub.on. After reaching a maximum, the
decrease in Co deposition with increased T.sub.on confirmed the
mass transfer effects observed in the rotating disk electrode
results. CE increased, reached a maximum and decreased with
increased T.sub.on (FIG. 140(b)).
[0617] q. Crystal Structure and Microstructures
[0618] FIG. 142 show the XRD (left) and the SEM (right) results of
deposits obtained at 25.degree. C. and 1000 mA/cm.sup.2 with
various T.sub.on. The (11.0) peak of Sm(OH).sub.3 was found in the
deposit obtained at T.sub.on, of 0.1 ms (FIG. 142(d)). With further
increased T.sub.on, Sm(OH).sub.3 peaks disappeared. At short
T.sub.on of 0.1 ms, (00.2), (10.0) and (11.0) peaks of hcp-Co
appeared in the deposit. When T.sub.on increased to 1 ms, only the
(10.0) peak was found. The change of deposit orientations with
increased T.sub.on is similar to DC electrodeposition at 60.degree.
C. Both of these changes were due to increased Sm deposit content.
Increased T.sub.on resulted in increased Sm content also leading to
significant decrease in microstructure size (FIG. 142, right).
Again, the dependence of crystal orientation and particle size on
Sm content was observed.
[0619] r. Magnetic Properties
[0620] The effects of T.sub.on on magnetic properties are shown in
FIG. 143. As discussed in previous sections: Ms values depended on
alloy composition and decreased linearly with increased Sm content
in agreement with sputtered films. Hc.perp. was higher than
Hc.parallel. and decreased with increasing Sm content (FIG.
143(c)). S.sub..parallel. were larger than S.perp. and both
decreased with increased Sm content (FIG. 143(d)).
[0621] s. Deposition Rates of Sm and Co
[0622] In the previous section, long periods (100 ms), short
T.sub.on (0.1-2 ms) and low duty cycles (0.001-0.02) examined the
effect of T.sub.on on Sm deposit content. Because short T.sub.on
consumed less metal ions in a single pulse and low duty cycle
provided greater relaxation time for the recovery of metal ion
concentrations, the metal ion concentration at the cathode surface
probably remain close to the bulk solution concentration just
before the beginning of each pulse. Therefore, we assumed that at
the initiation of each pulse the solution composition at the
cathode equaled the bulk solution. Thus, the deposit contents at
each pulse were identical, and Sm and Co in deposits were assumed
the result of the reduction of Sm and Co ions to metals rather than
to precipitation of Sm(OH).sub.3 and Co(OH).sub.2. This provided a
first approximation in the calculation of the electrodeposition
rates of Sm and Co.
[0623] The deposit content for each pulse was assumed to be
identical. Therefore, the amount of electrodeposited Sm and Co per
pulse at different T.sub.on can be calculated, as shown in Table
26. Electrodeposition rates at different time can be obtained by
taking the difference in deposit content (amount of Co and Sm) for
pulses and divided by the difference in time duration.
TABLE-US-00026 TABLE 26 Calculation of reaction rates of Sm and Co
Pulse Information Deposits for 50 C Deposits per Pulse Reaction
Rate Ton charge per pulse Sm Co Sm Co Time Sm Co (ms) pulse (C)
number (mole) (mole) (mole) (mole) (ms) (mole)/s (mole)/s 0.1
1.90E-04 263158 2.3E-08 2.8E-06 8.7E-14 1.1E-11 0.05 8.7E-10
1.1E-07 0.3 5.70E-04 87719 1.4E-07 5.0E-06 1.6E-12 5.7E-11 0.20
7.5E-09 2.3E-07 0.5 9.50E-04 52632 2.9E-07 7.6E-06 5.6E-12 1.4E-10
0.40 2.0E-08 4.4E-07 0.7 1.33E-03 37594 3.2E-07 7.1E-06 8.4E-12
1.9E-10 0.60 1.4E-08 2.2E-07 1.0 1.90E-03 26316 3.4E-07 6.7E-06
1.3E-11 2.5E-10 0.85 1.5E-08 2.2E-07 1.3 2.47E-03 20243 3.9E-07
6.6E-06 1.9E-11 3.3E-10 1.15 2.1E-08 2.4E-07 1.6 3.04E-03 16447
4.2E-07 6.3E-06 2.5E-11 3.8E-10 1.45 2.1E-08 1.9E-07 2 3.80E-03
13158 4.5E-07 6.0E-06 3.4E-11 4.5E-10 1.80 2.1E-08 1.8E-07 charge
per pulse (C) = PCD .times. area .times. T.sub.on = 0.5(A/cm.sup.2)
.times. 3.8 (cm.sup.2) .times. 0.0001 (sec) = 1.90E-04 pulse number
= total applied charge/charge per pulse = 50/1.90E-04 = 263158
Deposits for 50 C (total applied charge): Sm: 2.3E-08 (mole) and
Co: 2.8E-06 (mole) from AA and EDS Deposits per Pulse: Deposits for
50 C/pulse number, Sm = 2.3E-08/263158 = 8.7E-14 (mole) Co =
2.8E-06/263158 = 1.1E-11 (mole) Reaction Rate (at 0.05 ms):
Deposits per Pulse/Deposit duration, Sm = 8.7E-14/0.0001 = 8.7E-10
(mole/s) Co = 1.1E-11/0.0001 = 1.1E-07 (mole/s) Reaction Rate (at
0.2 ms = (0.1 ms + 0.3 ms)/2); Sm =
(1.6E-12-8.7E-14)/(0.0003-0.0001) = 7.5E-09 (mole/s) Co =
(5.7E-11-1.1E-11)/(0.0003-0.0001) = 2.3E-07 (mole/s)
[0624] The deposition rates of Sm and Co at various deposition
times are plotted in FIG. 144. Deposition rates of Sm increased
linearly with deposition time. On the other hand, the deposition
rate of Co increased, reached a maximum, and then decreased with
increased deposition time. Higher PCD of 1000 mA/cm.sup.2 resulted
in higher deposition rates of both Sm and Co compared to the lower
PCD of 500 mA/cm.sup.2. Higher PCD caused Co deposition rates to
reach a maximum in a shorter deposition time (0.3 ms for 1000
mA/cm.sup.2 and 0.4 ms for 500 mA/cm.sup.2). Co deposition rates
were much higher than Sm deposition rates (about 10-120 times
higher depending on PCD and deposition time) indicating that Co
deposition is faster than Sm in agreement with results on frequency
effects. The decrease in Co deposition rates after the maximum
indicates mass transfer effects in the electrodeposition of Co--Sm
alloys consistent with the results of rotating disk electrode
studies and the effect of T.sub.on.
[0625] It will be apparent to those skilled in the art that various
modifications and variations can be made in the present invention
without departing from the scope or spirit of the invention. Other
aspects of the invention will be apparent to those skilled in the
art from consideration of the specification and practice of the
invention disclosed herein. It is intended that the specification
and examples be considered as exemplary only, with a true scope and
spirit of the invention being indicated by the following
claims.
* * * * *