U.S. patent application number 10/938629 was filed with the patent office on 2005-02-10 for magnetic recording medium and producing method thereof.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Den, Tohru, Yasui, Nobuhiro.
Application Number | 20050031905 10/938629 |
Document ID | / |
Family ID | 26601115 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050031905 |
Kind Code |
A1 |
Yasui, Nobuhiro ; et
al. |
February 10, 2005 |
Magnetic recording medium and producing method thereof
Abstract
To provide a magnetic recording medium with good record and
reproduction characteristics. In the magnetic recording medium
having an anodic oxidized alumina nanohole film filled with a
magnetic substance, the anodic oxidized alumina nanohole film 13 is
formed on a substrate 16 with at least one base electrode layer 15
sandwiched therebetween, the base electrode layer 15 is a film that
has fcc structure and whose (111) face is oriented in the direction
perpendicularly to a substrate, and the fillers 14 in the alumina
nanoholes 10 have hcp structure and include hard magnetic substance
whose principal component is Co and whose c-axis is perpendicular
to the substrate.
Inventors: |
Yasui, Nobuhiro; (Kanagawa,
JP) ; Den, Tohru; (Tokyo, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
CANON KABUSHIKI KAISHA
TOKYO
JP
|
Family ID: |
26601115 |
Appl. No.: |
10/938629 |
Filed: |
September 13, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10938629 |
Sep 13, 2004 |
|
|
|
09964781 |
Sep 28, 2001 |
|
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Current U.S.
Class: |
428/693.1 ;
428/328; 428/675; G9B/5.306; G9B/5.307 |
Current CPC
Class: |
Y10T 428/1291 20150115;
G11B 5/858 20130101; Y10T 428/256 20150115; Y10T 428/12667
20150115; G11B 5/855 20130101; Y10T 428/12465 20150115; Y10T
428/325 20150115; Y10T 428/1275 20150115; Y10T 428/31 20150115;
Y10T 428/24479 20150115; Y10T 428/25 20150115 |
Class at
Publication: |
428/693 ;
428/328; 428/675 |
International
Class: |
B32B 005/16; G11B
005/64 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2000 |
JP |
298785/2000 |
Sep 27, 2001 |
JP |
296766/2001 |
Claims
1. A magnetic recording medium, in which a mainly aluminum layer
having holes on a substrate is filled with a magnetic substance,
comprising: at least one conductive layer between the mainly
aluminum layer and the substrate, wherein the magnetic substance
contacts the conductive layer and the magnetic substance includes a
hard magnetic substance that has hcp structure and the c-axes of
which are oriented in a direction perpendicular to the
substrate.
2. The magnetic recording medium according to claim 1, wherein the
hard magnetic substance includes Co.
3. The magnetic recording medium according to claim 2, wherein the
mainly aluminum layer has nanoholes formed by anodic
oxidization.
4. The magnetic recording medium according to claim 1, wherein the
conductive layer is a base electrode layer.
5. The magnetic recording medium according to claim 1, wherein the
conductive layer includes Cu as a component.
6. The magnetic recording medium according to claim 1, wherein a
portion of each of the fillers with which the holes are filled, the
portion which contacts the conductive layer, has fcc structure and
its (111) face is oriented in a direction perpendicular to the
substrate.
7. The magnetic recording medium according to claim 6, wherein the
portion touching the conductive layer includes Cu as a
component.
8. The magnetic recording medium according to claim 6, wherein the
portion touching the conductive layer includes NiFe as a
component.
9. The magnetic recording medium according to claim 2, wherein the
hard magnetic substance including Co includes at least one element
among Cu, Cr, P, Ni, Pt, and Pd.
10. The magnetic recording medium according to claim 1, wherein
materials from the conductive layer to the hard magnetic substance
are given epitaxial growth.
11. The magnetic recording medium according to claim 1, wherein a
soft magnetic substance layer is formed under the conductive
layer.
12. The magnetic recording medium according to claim 1, wherein the
holes are arranged in a honeycomb array.
13. The magnetic recording medium according to claim 1, wherein the
holes are arranged in a rectangular array.
14. A magnetic record and reproduction apparatus comprising the
magnetic recording medium according to claim 1.
15. A magnetic recording medium, in which an aluminum oxide layer
having holes on a substrate is filled with a magnetic substance,
comprising: at least one conductive layer between the aluminum
oxide layer and the substrate, wherein the conductive layer has fcc
structure and its (001) face is oriented in a direction
perpendicular to the substrate, and the magnetic substance includes
a hard magnetic substance that has L1.sub.0 structure and the
c-axes of which are oriented in the direction perpendicular to the
substrate.
16. The magnetic recording medium according to claim 15, wherein
the hard magnetic substance includes MPt (M=Co, Fe, Ni).
17. The magnetic recording medium according to claim 15, wherein
the conductive layer includes any one among Pt, Pd, Cu, Ir, and
Rh.
18. The magnetic recording medium according to claim 15, wherein a
portion of each of the fillers with which the holes are filled, the
portion which contacts the conductive layer, has fcc structure and
its (001) face is oriented in a direction perpendicular to the
substrate.
19. The magnetic recording medium according to claim 18, wherein
the portion contacting the conductive layer includes any one among
Pt, Pd, Cu, Ir, and Rh.
20. The magnetic recording medium according to claim 16, wherein
the hard magnetic substance including MPt (M=Co, Fe, Ni) includes
at least one element among Cu, Cr, P, Ag, and Pd.
21. The magnetic recording medium according to claim 16, wherein
materials from the conductive layer to the hard magnetic substance
including MPt (M=Co, Fe, Ni) are given epitaxial growth.
22. The magnetic recording medium according to claim 15, wherein an
MgO (001) layer is formed under the conductive layer.
23. The magnetic recording medium according to claim 15, wherein a
soft magnetic substance layer is formed under the conductive
layer.
24. The magnetic recording medium according to claim 15, wherein
the holes are arranged in a honeycomb array.
25. The magnetic recording medium according to claim 15, wherein
the holes are arranged in a rectangular array.
26. A magnetic record and reproduction apparatus comprising the
magnetic recording medium according to claim 15.
27. A magnetic recording medium, in which an aluminum oxide layer
having holes on a substrate is filled with a magnetic substance,
comprising: at least one conductive layer between the aluminum
oxide layer and the substrate, wherein the conductive layer has any
one of L1.sub.0, L1.sub.1, and L1.sub.2 ordered structures, and its
square array face is oriented in a direction perpendicular to the
substrate, and the magnetic substance includes a hard magnetic
substance that has the L1.sub.0 structure and the c-axes of which
are oriented in the direction perpendicular to the substrate.
28. The magnetic recording medium according to claim 27, wherein
the hard magnetic substance includes MPt (M=Co, Fe, Ni).
29. The magnetic recording medium according to claim 28, wherein
the conductive layer has any one among L1.sub.0 ordered structure
including MPt (M=Co, Fe, Ni), L1.sub.1 ordered structure including
CuPt, and L1.sub.2 ordered structure including CoPt.sub.3.
30. The magnetic recording medium according to claim 28, wherein
the hard magnetic substance including MPt (M=Co, Fe, Ni) includes
at least one element among Cu, Cr, P, Ag, and Pd.
31. The magnetic recording medium according to claim 28, wherein
materials from the conductive layer to the hard magnetic substance
including MPt (M=Co, Fe, Ni) are given epitaxial growth.
32. The magnetic recording medium according to claim 27, wherein an
MgO (001) layer is formed under the conductive layer.
33. (Cancelled)
34. The magnetic recording medium according to claim 27, wherein
the holes are arranged in a honeycomb array.
35. The magnetic recording medium according to claim 27, wherein
the holes are arranged in a rectangular array.
36. A magnetic record and reproduction apparatus comprising the
magnetic recording medium according to claim 27.
37. A method of manufacturing a magnetic recording medium that has
a film with anodic oxidized alumina nanoholes filled with a
magnetic substance, comprising: a step of preparing a substrate; a
step of forming a conductive layer, which has fcc structure and its
(111) face is oriented in a direction perpendicular to the
substrate, on the substrate, and forming an alumina layer thereon;
a step of anodizing the alumina layer and forming alumina
nanoholes; and a step of electrodepositing a hard magnetic
substance layer, which has hcp structure containing Co in the
alumina nanoholes while the c-axes are oriented in a direction
perpendicular to the substrate, in the alumina nanoholes.
38. The method of manufacturing a magnetic recording medium
according to claim 37, further comprising a step of
electrodepositing a nonmagnetic layer, which has fcc structure
including Cu and whose (111) face is oriented in a direction
perpendicular to the substrate, before the step of
electrodepositing the hard magnetic substance layer.
39. The method of manufacturing a magnetic recording medium
according to claim 37, further comprising a step of
electrodepositing a soft magnetic layer, which has fcc structure
mainly including NiFe and whose (111) face is oriented in a
direction perpendicular to the substrate, before the step of
electrodepositing the hard magnetic substance layer.
40. A method of manufacturing a magnetic recording medium that has
a film with anodic oxidized alumina nanoholes filled with a
magnetic substance comprising: a step of preparing a substrate; a
step of forming a conductive layer, which has fcc structure and
whose (001) face is oriented in a direction perpendicular to the
substrate, and an alumina layer on the substrate; a step of forming
alumina nanoholes by anodizing the alumina layer; a step of
electrodepositing a layer including Mpt (M=Co, Fe, Ni) in each of
the alumina nanoholes; and a step of formation of hard magnetic
substance oriented the c-axes in a direction perpendicular to the
substrate in L1.sub.0 ordered structure by annealing process.
41. A method of manufacturing a magnetic recording medium that has
a film with anodic oxidized alumina nanoholes filled with a
magnetic substance comprising: a step of preparing a substrate; a
step of forming a conductive layer, which has any one of L1.sub.0,
L1.sub.1, and L1.sub.2 ordered structure, and a square lattice face
of which is oriented in a direction perpendicular to the substrate,
and an alumina layer on the substrate; a step of anodizing the
alumina layer and forming alumina nanoholes; a step of
electrodepositing a layer including Mpt (M=Co, Fe, Ni) in each of
the alumina nanoholes; and a step of formation of hard magnetic
substance oriented the c-axes in a direction perpendicular to the
substrate in L1.sub.0 ordered structure by annealing process.
42. The method of manufacturing a magnetic recording medium
according to claim 40, further comprising a step of
electrodepositing a nonmagnetic layer, which has fcc structure
including any one among Pt, Pd, Cu, Ir, and Rh, and whose (001)
face is oriented in a direction perpendicular to the substrate,
before the step of electrodepositing the layer including Mpt (M=Co,
Fe, Ni) in each of the alumina nanoholes.
43. The method of manufacturing a magnetic recording medium
according to claim 41, further comprising a step of
electrodepositing a soft magnetic layer, which has fcc structure
mainly including NiFe and whose (001) face is oriented in a
direction perpendicular to the substrate, before the step of
electrodepositing the layer including Mpt (M=Co, Fe, Ni) in each of
the alumina nanoholes.
44. The magnetic recording medium according to claim 1, wherein the
conductive layer has fcc structure and its (111) face is oriented
in a direction perpendicular to the substrate.
45. The magnetic recording medium according to claim 1, wherein the
layer is an alumina oxide layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a magnetic recording medium
and a production method thereof, and in particular, to a
perpendicular magnetic recording medium, where reproduction noise
is low and high density recording is possible, and a production
method thereof.
[0003] 2. Related Background Art
[0004] Increase in information recording capacity of magnetic disk
units and the like is desired with sharp increase of information
processing in recent years. In particular in hard disk drives, an
information-recording amount per unit area is now increasing with
an annual rate of 60% or more. The information-recording amount is
desired to continue to increase, and miniaturization and a higher
density are also desired for use as a portable recording device and
the like.
[0005] In a magnetic recording medium for a hard disk drive used
conventionally, a longitudinal magnetic recording method is
adopted, and magnetization is recorded in parallel to a disk
surface. In this longitudinal magnetic recording method, it is
necessary to thin a magnetic recording layer to generate a magnetic
field upward from the medium so as to suppress an anti-magnetic
field in each magnetic domain and to detect a magnetization state,
with high densification. Therefore, a volume of a magnetic particle
becomes extremely small, resulting in the tendency of easily
bringing a superparamagnetic effect. Thus, it may happen that
energy stabilizing a magnetizing direction becomes lower than
thermal energy, magnetization recorded changes with time, and
finally record is erased. For this reason, in recent years,
researches shifting to perpendicular magnetic recording methods
where the film thickness of a recording layer can be made to be
large have been active instead of the longitudinal magnetic
recording method.
[0006] As media for perpendicular magnetic recordings, a monolayer
type of medium having a single layer of magnetic recording layer,
and a two-layer type of medium having a hard magnetic recording
layer on a soft magnetic layer with high permeability that is a
backing layer are proposed. In the case of the latter, a magnetic
circuit is constituted, the magnetic circuit where a magnetic
field, which is concentrated from a perpendicular magnetic head to
the recording layer, is returned to the head through horizontally
passing the soft magnetism layer. Although effects of increasing a
recording magnetic field and enhancing record and reproduction are
expected in this two-layer type of medium having the backing layer,
it is also pointed out that there is a problem that a reversal of
magnetization of the soft magnetic layer, and noise accompanying
domain wall transfer, etc. are caused.
[0007] This will be described in detail below with using an
explanatory diagram of a conventional perpendicular magnetic
recording medium in FIGS. 2A and 2B. It is possible to use a glass
substrate, an aluminum substrate, a carbon substrate, a plastic
substrate, a Si substrate, etc. can be used as a substrate 21. In
the case of the aluminum substrate, in order to secure hardness, as
shown in FIGS. 2A and 2B, a NiP layer 22 is produced in many cases
as a base layer by plating etc. As a backing layer 23, a NiFe alloy
(permalloy) with high permeability etc. is used at the thickness of
several .mu.m to several tens .mu.m. Generally, as a recording
layer 24, a Co--Cr alloy is used. When being produced by
sputtering, a recording layer 24 grows up in a state where a core
portion 26 with much Co composition, and a shell portion 27 with
comparatively much Cr composition around the core portion 26 are
separated as shown in FIG. 2B. The core portion 26 has the
hexagonal close-packed structure (hereinafter hcp structure) having
an approximately cylindrical shape, and becomes hard magnetic to
become a recording portion. The shell portion 27 becomes soft
magnetic or non-magnetic due to much Cr composition, and also plays
the role of weakening the interaction between adjacent core
portions. In the core portion 26, since the c-axis faces in the
direction perpendicularly to the substrate, magnetization turns in
the direction perpendicularly to the substrate due to the action of
crystal magnetic anisotropy. Ta, Pt, Rh, Pd, Ti, Nb, Hf, and the
like are added besides Co--Cr in the above-described recording
layer 24.
[0008] In addition, although this is not shown in FIGS. 2A and 2B,
a base layer is formed between the recording layer 24 and backing
layer 23 in order to enhance the crystallinity of the recording
layer 24. Alternatively, in order to weaken a little the magnetic
bond of the recording layer 24 and backing layer 23, a base layer
such as an oxide layer is formed (refer to Japanese Patent
Application Laid-Open No. 7-73429).
[0009] It is common to thinly form a protection layer 25 on its
surface, and carbon, carbide, nitride, and the like have been
examined as materials.
[0010] Next, since the present invention uses anodic oxidized
alumina having fine pores, an anodic oxide film and an alumite
magnetic substance with the anodic oxidized film will be described
in detail below with using FIGS. 3A and 3B. The term. "anodic
oxidized alumina" means a product through an anodic oxidization of
aluminum.
[0011] When an aluminum substrate 31 is anodized in an acid
electrolyte such as a sulfuric acid, oxalic acid, and phosphoric
acid electrolyte, an anodic oxidized film 32 which is a porous
anodic oxidized film as shown in FIG. 3A is formed (for example,
refer to R. C. Furneaux, W. R. Rigby & A. P. Davidson,
"NATURE", vol. 337, p.147 (1989) or the like). The characteristic
of this porous film is to have specific geometric structure that
extremely fine cylindrical pores (alumina nanoholes 33) whose
diameter 2r is several nm to several hundreds nm are arranged in
parallel at intervals of several tens nm to several hundreds nm
(2R)). This cylindrical pore has a high aspect ratio, and is also
excellent in the uniformity of cross sectional diameters.
[0012] In addition, it is possible to control the structure of the
porous film to some extent by changing the conditions of anodic
oxidation. For example, it is known that it is possible to control
to some extent pore intervals with an anodic oxidation voltage, the
depth of pores by anodic oxidation time, and diameters of the pores
by pore-widening treatment. Here, the pore-widening treatment is
the etching of alumina, where wet etching with phosphoric acid is
usually used.
[0013] In addition, in order to improve the perpendicularity,
linearity, and independence of pores in the porous film, a method
of two-step anodic oxidation is proposed, that is, the method which
produces a porous film having pores exhibiting better
perpendicularity, linearity, and independence by performing again
anodic oxidation after once removing a porous film formed by
performing anodic oxidation ("Japanese Journal of Applied Physics",
Vol. 35, Part 2, No. 1B, pp. L126-L129, Jan. 15, 1996). Here, this
method uses a phenomenon that hollows of the surface of the
aluminum substrate that are formed when the anodic oxide film
formed by the first anodic oxidation is removed become starting
points for forming the pores of the second anodic oxidation.
[0014] Furthermore, in order to improve the controllability of
shape, intervals, and a pattern of pores in a porous film, a method
of forming starting points of pores with using stamping, that is, a
method is also proposed, the method which is for producing a porous
film having pores showing the controllability of better shape,
intervals, and a pattern by performing anodic oxidation after
forming hollows, which are formed by pressing a substrate, having a
plurality of projections on its surface, on the surface of an
aluminum substrate, as starting points of pores (Japanese Patent
Application Laid-Open No. 10-121292 or Masuda, "solid physics" 31,
493 (1996)). In addition, the technology for forming pores that are
not honeycomb structure but concentric shape is reported by Okubo
et al. in Japanese Patent Application Laid-Open No. 11-224422.
[0015] As shown in FIG. 3A, an insulating layer made of thick
aluminum oxide is formed in each bottom of the above-described
alumina nanoholes 33. Since electrodeposition into nanoholes is
difficult if there is this insulating layer, a method of thinning
the insulating layer in each bottom of the nanoholes, that is, a
method called an electric current recovery method is generally
adopted. The electric current recovery method is a method of
thinning the insulating layer in each bottom by gradually lowering
an anodic oxidation voltage. However, since each thin insulating
layer remains by this method, alternating current electrodeposition
with nearly 10 to 50 V of high voltage becomes necessary for the
electrodeposition into nanoholes. Since there is limitation in
structure control of electrodeposition inclusion objects in the
electrodeposition with such a high voltage, polycrystals are
usually electrodeposited unevenly. Thus, even if Co is
electrodeposited, it is impossible to evenly grow the c-axis, which
is an axis where magnetization is easy, in the direction
perpendicular to the substrate (refer to "I-EEE Trans. Mag." vol.
26, 1635 (1990), and the like). In addition, since the thickness
and shape of insulating layers in bottoms of nanoholes are uneven,
portions not electrodeposited are apt to arise as shown in FIG. 3B.
Referring to FIG. 3B, an electrodeposited magnetic substance is
indicated by 34, and an extended portion by 35.
[0016] There is much dispersion in the shape of particles,
including MPt (M=Co, Fe, Ni), which has Co and L1.sub.0 ordered
structure, as a component in the above-described conventional
recording layer formed by sputtering. It is said that, in a medium
for perpendicular magnetic recording, the dispersion of coercivity
normalized mainly with saturating magnetization and an average
coercivity determines characteristics. Thus, the dispersion of
particles in the size of MPt (M=Co, Fe, Ni) microcrystals that have
Co and the L1.sub.0 ordered structure is reflected in the
dispersion of the coercivity of the particles as it is, and
deteriorates the characteristics as a recording medium. Of course,
the dispersion in orientations of crystallographic axes of the
microcrystals is also a cause of the deterioration of the
characteristics.
[0017] In addition, it is difficult to fill the pores with the
above-described alumite magnetic substance, and it is not possible
to control the crystal orientation of magnetic substances, and in
particular, to control c-axis orientation. Furthermore, it is
insufficient to control an amount of electrodeposition inside each
pore.
[0018] An object of the present invention is to provide a
perpendicular magnetic recording medium that has uniform crystal
orientation to an anodic oxidation alumina layer, and in
particular, the c-axis orientation of Co, a Co alloy, and MPt
(M=Co, Fe, and Ni) having the L1.sub.0 ordered structure.
[0019] In addition, another object of the present invention is to
provide a perpendicular magnetic recording medium with good record
and reproduction characteristics, in which record particles are
shaped like pillars and variations in the shapes thereof are
reduced.
[0020] Furthermore, still another object of the present invention
is to provide an effective backing layer that enhances record and
reproduction characteristics.
[0021] Moreover, further still another object of the present
invention is to provide a method of easily manufacturing the
above-described magnetic recording medium, and to provide a
magnetic record and reproduction apparatus where the
above-described magnetic recording medium is used.
SUMMARY OF THE INVENTION
[0022] Namely, a first aspect of the present invention is a
magnetic recording medium characterized in that the magnetic
recording medium has pores filled with a magnetic substance, a
layer mainly made of aluminum oxide having the pores, and a
substrate holding the layer mainly made of aluminum oxide, wherein
one or more conductive layers are formed between the
above-described layer mainly made of aluminum oxide having the
pores and the above-described substrate, wherein the conductive
layer is a layer which has fcc structure and whose (111) face is
oriented in the direction perpendicular to the substrate, and
wherein the above-described magnetic substance includes a hard
magnetic substance that has hcp structure and is mainly made of Co
whose c-axes are perpendicular to the substrate.
[0023] In addition, a second aspect of the present invention is a
magnetic recording medium characterized in that the magnetic
recording medium has pores filled with a magnetic substance, a
layer mainly made of aluminum oxide having the pores, and a
substrate holding the layer mainly made of aluminum oxide, wherein
one or more conductive layers are formed between the
above-described layer mainly made of aluminum oxide having the
pores and the above-described substrate, wherein the conductive
layer is a layer which has fcc structure and whose (001) face is
oriented in the direction perpendicular to the substrate, and
wherein the above-described magnetic substance includes a hard
magnetic substance that has L1.sub.0 structure and c-axes oriented
in a direction perpendicular to the substrate.
[0024] Furthermore, a third aspect of the present invention is a
magnetic recording medium characterized in that the magnetic
recording medium has pores filled with a magnetic substance, a
layer mainly made of aluminum oxide having the pores, and a
substrate holding the layer mainly made of aluminum oxide, wherein
one or more conductive layers are formed between the
above-described layer mainly made of aluminum oxide having the
pores and the above-described substrate, wherein the
above-described conductive layer has any one of L1.sub.0, L1.sub.1,
and L1.sub.2 ordered structure, and a square lattice face of the
conductive layer is oriented in a direction perpendicular to the
substrate, and wherein the above-described magnetic substance
includes a hard magnetic substance that has L1.sub.0 structure and
c-axes oriented in a direction perpendicular to the substrate.
[0025] In addition, a fourth aspect of the present invention is a
magnetic record and reproduction apparatus using the
above-described magnetic recording medium.
[0026] Furthermore, a fifth aspect of the present invention is a
method of manufacturing a magnetic recording medium that has a film
with anodic oxidized alumina nanoholes filled with a magnetic
substance, comprising a step of forming a base electrode layer,
which has fcc structure and whose (111) face is oriented in a
direction perpendicular to the substrate, and an aluminum layer on
a substrate, a step of forming alumina nanoholes by anodizing the
aluminum layer, and a step of electrodepositing a hard magnetic
substance layer, which is mainly made of Co and has hcp structure,
in the alumina nanoholes with orienting the hard magnetic substance
layer in the c-axis to the direction perpendicular to the
substrate.
[0027] Moreover, a sixth aspect of the present invention is a
method of manufacturing a magnetic recording medium that has a film
with anodic oxidized alumina nanoholes filled with a magnetic
substance, comprising a step of forming a base electrode layer,
which has fcc structure and whose (001) face is oriented in a
direction perpendicular to the substrate, and an aluminum layer on
a substrate, a step of forming alumina nanoholes by anodizing the
aluminum layer, a step of electrodepositing a hard magnetic
substance layer, which has L1.sub.0 ordered structure, in each of
the above-described alumina nanoholes, and a step of orienting the
above-described hard magnetic substance in the c-axis to a
direction perpendicular to the substrate.
[0028] In addition, a seventh aspect of the present invention is a
method of manufacturing a magnetic recording medium that has a film
with anodic oxidized alumina nanoholes filled with a magnetic
substance, comprising a step of forming a conductive layer, which
has any one of L1.sub.0, L1.sub.1, and L1.sub.2 ordered structure,
and a square lattice face of which is oriented in a direction
perpendicular to the substrate, and an aluminum layer on the
substrate, a step of forming alumina nanoholes by anodizing the
aluminum layer, a step of electrodepositing a hard magnetic
substance layer, which has L1.sub.0 ordered structure, in each of
the above-described alumina nanoholes, and a step of orienting the
above-described hard magnetic substance in the C-axis to a
direction perpendicular to the substrate.
BRIEF DESCRIPTION OF THE INVENTION
[0029] FIG. 1 is a schematic diagram showing an example of an
embodiment of a magnetic recording medium according to the present
invention;
[0030] FIGS. 2A and 2B are schematic diagrams showing an example of
conventional technology in a magnetic recording medium;
[0031] FIGS. 3A and 3B are schematic diagrams showing an example of
conventional technology in alumina nanoholes;
[0032] FIGS. 4A, 4B, 4C, 4D and 4E are schematic diagrams relating
to fillers in the present invention;
[0033] FIGS. 5A, 5B and 5C are schematic diagrams showing
comparison between the different orientation of the fillers;
[0034] FIGS. 6A and 6B are schematic diagrams showing states of the
magnetic recording medium after magnetic recording;
[0035] FIG. 7 is a schematic diagram showing a magnetic recording
apparatus using a magnetic recording medium according to the
present invention; and
[0036] FIGS. 8A, 8B and 8C are schematic diagrams showing the
crystal structure of various types of ordered structures.
DETAILED DESCRIPTION OF THE INVENTION
[0037] <Structure of a Magnetic Recording Medium>
[0038] A magnetic recording medium according to the present
invention will be described on the basis of drawings. FIG. 1 is a
schematic diagram showing the structure of a magnetic recording
medium according to the present invention.
[0039] In FIG. 1, reference numeral 10 denotes a nanohole (pore),
numeral 11 denotes a nanohole (pore) interval, and numeral 12
denotes a nanohole (pore) diameter. Furthermore, numeral 13 denotes
a layer (alumina) mainly made of aluminum oxide, numeral 14 denotes
fillers, numeral 15 denotes a base electrode layer (conductive
layer), and numeral 16 denotes a substrate (substrate holding the
layer 13 mainly made of aluminum oxide).
[0040] In the present invention, it is required for high-density
recording and sufficient signal detection to fill the alumina
nanoholes (pores) 10 with the fillers 14, each of which consists of
a hard magnetic substance mainly made of pillar-shaped Co or MPt
(M=Co, Fe, Ni) which has L1.sub.0 ordered structure. It is
preferable that the nanohole diameter 12 is in the range of several
nm to several hundred nm, and that an aspect ratio of a nanohole is
approximately two to ten. Although a circle, an ellipse, and a
rectangle can be used for the cross-sectional shape of each
nanohole, it is preferable that cross-sections of respective
nanoholes are the same. Furthermore, it is desirable that the shape
of each hole of the alumina nanoholes is cylinder-like, and stands
linearly and perpendicularly to the base electrode.
[0041] For producing the anodic oxidized alumina nanoholes used for
a perpendicular magnetic recording medium, it is very effective to
use an aluminum anodic oxidation method that is a method of
producing nanoholes, aspect ratio of which is large, with
sufficient controllability. The term "anodic oxidation" means an
oxidization caused at an anode in an acid solution. The nanohole
diameter 12 can be controlled from several nm to several hundreds
nm in the aluminum anodic oxidation, and in addition, the nanohole
interval 11 can be also controlled from a value, a little larger
than the nanohole diameter 12, to nearly 500 nm. Although various
kinds of acids can be used for the aluminum anodic oxidation, it is
preferable to use a sulfuric acid bath for producing nanoholes at
small intervals, a phosphoric acid bath for producing nanoholes
with comparatively large intervals, and an oxalic acid bath for
producing nanoholes therebetween. It is possible to expand the
nanohole diameter 12 by etching in a solution such as a phosphoric
acid solution after the anodic oxidation.
[0042] For producing nanoholes regularly, as described above, it is
effective to use the method of producing hollows, which become
starting points of formation of nanoholes, on an aluminum surface,
or the two-step anodic oxidation method. As a nanohole array used
for the present invention, it is preferable to be a honeycomb array
as shown in FIG. 5A, a rectangular array, or a square array, which
is a special case of the rectangular array.
[0043] Although aluminum is generally used as the above-described
anode-oxidized layer, other elements may be included as long as the
layer is mainly made of aluminum and can be anodized. A vacuum
deposition method by resistance heating, a sputtering method, CVD,
etc. can be used for forming this aluminum layer. However, it is
not preferable that the method cannot form a film having a surface
flattened to some extent.
[0044] Although a vacuum deposition method, a sputtering method,
etc. can be used for embedding fillers in the above-described
nanoholes, an electrodeposition method is preferable for embedding
the fillers in the pores each aspect ratio of which is large. In
order to produce a stacked film by the electrodeposition method, it
is possible to use a method of performing pulse electrodeposition
in a solution containing ions with different electrolytic
potentials besides a method of changing electrodeposition liquid in
the middle of electrodeposition. The following method can be used.
Thus, ions with low electrolytic potentials such as Pt, Cu, and Ni
are added in a small ratio to an electrodeposition solution where
Co ions with high electrolytic potentials are included. Then, after
depositing only the ions with low electrolytic potentials at a low
voltage, Co ions with high concentration are deposited at a high
voltage. It is also good to perform heat treatment after forming
the stacked film by the pulse electrodeposition at the time of
forming MPt (M=Co, Fe, Ni) having L1.sub.0 ordered structure.
[0045] In addition, various kinds of metal can be used as the base
electrode layer 15 for the above-described anodic oxidized alumina
nanoholes. However, if the base electrode layer has fcc structure,
it is preferable to use Pt, Pd, Cu, Ir, Rh, or an alloy thereof,
from a viewpoint of electrodeposition controllability for producing
a stacked film by the electrodeposition method. In particular, the
base metal's (111) face is orientated in a direction perpendicular
to the substrate in order to produce Co and a Co alloy, which have
hcp structure, in the nanoholes by the electrodeposition with
orienting the c-axes of the Co and Co alloy in a direction
perpendicular to the substrate. In addition, as long as a range is
within the limits where this orientation is obtained, one or more
components out of W, Nb, Pt, Si, O, and the like may be also
included in addition to Cu that is a principal component. When the
base electrode layer has L1.sub.0 orderd structure, and the c-axes
of which are oriented perpendicular to the substrate, the base
electrode's (001) face is oriented in a direction perpendicular to
the substrate. And a range of the direction is within the limits
where this orientation is obtained, one or more components out of
W, Nb, Ti, Si, O, and the like may be also included in addition to
Pt, Pd, Cu, Ir and Rh components.
[0046] A film may be used as the base electrode, the film which has
any one of L1.sub.0, L1.sub.1 or L1.sub.2 ordered structure whose
(001) face is oriented in a direction perpendicular to the
substrate, and whose square lattice face is oriented in a direction
perpendicular to the substrate. Specifically, it is possible to
select any one of L1.sub.0 whose principal component is MPt (M=Co,
Fe, Ni), FePd, TiAl, or CuAu; L1.sub.1 whose principal component is
CuPt; and L1.sub.2 whose principal component is Cu.sub.3Au,
Al.sub.3Ti, FePd.sub.3, Ni.sub.3X (X=Fe, Mn, Al), Pt.sub.3X (X=Co,
Fe, Mn, Ag, Al), or PtX.sub.3 (X=Ag, Au, Fe, Mn, Ni).
[0047] In addition, in the present invention, the hcp structure is
an abbreviation for hexagonal close-packed structure, and the fcc
structure is an abbreviation for face-centered cubic lattice
structure (face centered cubic).
[0048] Furthermore, the L1.sub.0 ordered structure is the structure
shown in FIG. 8A, the L1.sub.1 ordered structure is the structure
shown in FIG. 8B, and the L1.sub.2 ordered structure is the
structure shown in FIG. 8C.
[0049] Moreover, the possible structure of the above-described
fillers 14 is, from the top to a junction with the base electrode,
a hard magnetic substance (FIG. 4A), a hard magnetic substance/a
nonmagnetic substance (FIG. 4B), a hard magnetic substance/a soft
magnetic substance (FIG. 4C), a hard magnetic substance/a soft
magnetic substance/a nonmagnetic substance (FIG. 4E), or a hard
magnetic substance/a nonmagnetic substance/a soft magnetic
substance (FIG. 4D).
[0050] Here, the hard magnetic substance has the hcp structure
where the c-axis is oriented in a direction perpendicular to the
substrate, and the nonmagnetic substance and soft magnetic
substance have the fcc structure where the (111) face is oriented
in the direction perpendicular to the substrate. In addition, a
hard magnetic substance portion may have Co as a principal
component, and may also include one or more components out of Cu,
Cr, P, Ni, Pt, and Pd. Furthermore, it is preferable that a
nonmagnetic substance portion has fcc structure with having Cu, Pt,
Pd, Ir, Rh as a principal component, and the (111) face thereof is
oriented in the direction perpendicular to the substrate. Moreover,
one or more components out of W, Nb, Si, O, etc. may be also
included in addition to Pt, Pd, Cu, Ir, Rh that is a principal
component. In addition, the soft magnetic substance portion has
NixFe (1-x) as a principal component, and it is desirable that a
range of X is 0.65 to 0.91. Furthermore, the soft magnetic
substance may also include Co, Cr, P, Pt, Ag, Pd, etc. in part.
[0051] Moreover, the hard magnetic substance is characterized in
that the hard magnetic substance has the L1.sub.0 ordered structure
where the c-axis is oriented in the direction perpendicular to the
substrate, and that the nonmagnetic substance and soft magnetic
substance has the fcc structure where the (001) face is oriented in
the direction perpendicular to the substrate. In addition, a hard
magnetic substance portion has MPt (M Co, Fe, Ni) as a principal
component, and may include one or more components out of Cu, Cr, P,
Ag, and Pd. Furthermore, a nonmagnetic substance portion has Pt,
Pd, Cu, Ir, and Rh as principal components with having the fcc
structure, and it is preferable that the (001) face is oriented in
the direction perpendicular to the substrate. One or more
components out of W, Nb, Ti, Si, O, and the like may be also
included in addition to Pt, Pd, Cu, Ir and Rh components that are
principal ones. In addition, the soft magnetic substance portion
has NixFe (1-x) as a principal component, and it is desirable that
a range of X is 0.65 to 0.91. Furthermore, the soft magnetic
substance may also include Co, Cr, P, Pt, Ag, Pd, etc. in part.
[0052] Furthermore, the above-described fillers 14 are made by
performing epitaxial growth. This means the growth of the fillers
14 with crystal orientation being kept while being affected by the
face (111) of the fcc structure, or the square lattice face of the
L1.sub.0 ordered structure, L1.sub.1 ordered structure, or L1.sub.2
ordered structure of the base electrode layer. An example of the
square lattice face is (002) face of the L1.sub.0 ordered
structure. This does not deny the case of not being a single
crystal, the case of lattice mismatching with the conductive layer,
or the like. Furthermore, it is also possible to highly orient the
c-axis of the L1.sub.0 ordered structure in the direction
perpendicular to the substrate by heat treatment.
[0053] In addition, as alumina nanoholes, it is preferable that the
nanohole interval 11 and the nanohole diameter 12 are uniform, and
that the alumina nanoholes are arranged regularly in a honeycomb or
square shape. In particular, this is important when the medium is
used as a patterned medium. Furthermore, it is desirable that the
shape of each hole of the alumina nanoholes is cylinder-like, and
stands linearly and perpendicularly to the base electrode.
[0054] As the above-described substrate 16, glass, aluminum,
carbon, plastic, Si, etc. can be used. In the case of an aluminum
substrate, in order to secure hardness, it is desirable to form a
NiP film as a base layer by plating etc. Furthermore, it is
preferable to use an MgO substrate or to form an MgO film on the
above-mentioned substrate when the square lattice face of a
material used as the above-described base electrode layer is
oriented in the direction perpendicular to the substrate. In
addition, it is also effective to form a soft magnetic layer as a
backing layer between the substrate 16 and base electrode layer 15.
For backing layer, a film containing NixFe (1-x) as a principal
component can be used, and it is desirable that a range of X is
0.65 to 0.91. Furthermore, the soft magnetic substance may also
include Co, Cr, P, Pt, Pd, etc. in part. Furthermore, the stacked
sequence can be an MgO layer, a soft magnetic backing layer, and a
conductive layer from the bottom, or a soft magnetic backing layer,
an Mgo layer, and a conductive layer. Although it is preferable
that the (001) face of the soft magnetic layer is oriented in the
case of NixFe (1-x), the soft magnetic layer can be in an amorphous
state or another state since other soft magnetic substances can be
also adopted.
[0055] In addition, a top face of a magnetic recording medium is
given precision polishing with using diamond slurry etc., and the
Rms (Root mean square) is 1 nm or less. Furthermore, a protection
layer can be also formed on the surface, and it is possible to use
nonmagnetic substances such as carbide and nitride besides carbon
so as to give wear-proof property against friction with a head. In
particular, a magnetic recording medium of the present invention is
effective as a perpendicular magnetic recording medium. In order to
provide a magnetic recording apparatus, it is required to
incorporate a read/write head, drive control devices such as a
motor, a signal processing circuit, a dust-proof case, and the like
in addition to the above-described medium as shown in FIG. 7.
Referring to FIG. 7; the magnetic recording medium is indicated by
71, the driving portion for magnetic recording medium by 72, the
magnetic head by 73, and the driving portion for magnetic head by
74. However, in a magnetic record and reproduction apparatus, the
driving of a magnetic recording medium is not limited to only the
rotation and the driving of a magnetic head is not limited to only
the slide on a periphery.
EXAMPLES
[0056] The present invention will be specifically described with
reference to the following examples.
Example 1
[0057] This example relates to a manufacturing method and
respective shapes and orientation of a hard magnetic substance
filling anodic oxidized alumina nanoholes.
[0058] A substrate on which a Ti film of 10 nm thick and a Cu film
of 20 nm thick, and an aluminum film of 500 nm thick had been
formed on Si substrate by sputtering was anodized by applying 40 V
in 0.3 M of oxalic acid aqueous solution at 16.degree. C. Next, the
substrate was immersed for 25 minutes in 0.5wt% of phosphoric acid
aqueous solution for expanding hole diameters. At this time, the
(111) face of the Cu film was oriented in the direction
perpendicular to the substrate, and since a Cu face was exposed in
each nanohole bottom, the Cu film had good conductivity.
[0059] The anodic oxidized alumina nanoholes thus produced was
filled with Co, which is a hard magnetic substance. Here, an
aqueous solution that consists of cobalt sulfate (II) heptahydrate
of 0.2 M and boric acid of 0.3 M was used at 24.degree. C. for the
electrodeposition of Co.
[0060] The electrodeposition was performed in the above-described
solution with using Ag/AgCl as a reference electrode in each case
of -2.0 V, -1.5 V, and -1.0 V. Furthermore, the electrodeposited
materials that overflowed on the surface were ground and removed
from these samples with using the diamond slurry of 1/4 .mu.m. At
this time, surface Rms was 1 nm or less.
[0061] When the above samples were observed with an FE-SEM, the
fillers exist in all nanoholes. It was verified that the linearity
of nanoholes was also excellent through the observation from cross
sections.
[0062] Furthermore, the results of X-ray diffractometry of the
samples produced are shown in the following Table 1. A sample S was
powder, whose data was derived from JCPDS cards. The intensity
ratios are ratios of integrated intensities.
1 TABLE 1 Sample S Sample A Sample B Sample C Applied Voltage -2.0
V -1.5 V -1.0 V (vs Ag/AgCl) X-ray diffraction 0.6 0.61 1.28 5.31
intensity ratio (002)/(101) X-ray diffraction 0.2 0.08 0.12 0.73
intensity ratio (100)/(101)
[0063] As the result of X-ray diffractometry of the samples filled
with Co, it was verified that the (002) diffraction intensity
increases in the direction perpendicular to the substrate by
lowering an applied voltage, and c-axes of samples A to C proceeded
to be oriented. It is conceivable that the slower deposition
velocity of the fillers is better from the viewpoint of voltage
dependency, the deposition velocity that can be estimated to be
almost 3 nm/sec.
[0064] As described above, it is possible to form the fillers with
high orientation into nanoholes when velocity is slow.
Example 2
[0065] This example relates to the formation of an alloy of Co and
Cu by mixing the electrodeposition liquid in Example 1 and a copper
sulfate (II) aqueous solution.
[0066] First, similarly to Example 1, the alumina nanoholes were
prepared.
[0067] An aqueous solution that a copper sulfate (II) pentahydrate
of 0.01 M was mixed with an aqueous solution, which consists of
cobalt sulfate (II) heptahydrate of 0.2 M and boric acid of 0.3 M,
in a 1:1 ratio was used at 24.degree. C. for the
electrodeposition.
[0068] The electrodeposition was performed with applying -1.0 V to
the Ag/AgCl reference electrode.
[0069] Then, electrodepositions overflowed on the surface were
removed by polishing, and X-ray diffractometry and magnetization
measurement were performed.
[0070] As the result of X-ray diffraction, it was verified that the
c-axes of electrodepositions are oriented dominantly.
[0071] Furthermore, although the saturation magnetization of this
ample decreased to 680 (emu/cc) than the case of only Co according
to magnetization measurement at 24.degree. C., the remanence ratio
of the magnetic hysteresis curve in the direction perpendicular to
the substrate became good to 0.94, which was improved by 5%.
[0072] As described above, the effects by alloying of Co were
found.
Example 3
[0073] This example relates to a manufacturing method and
orientation of a nonmagnetic substance and soft magnetic substance
portions in the structure of fillers, and the orientation of a hard
magnetic substance portion caused by the result.
[0074] First, possible structure of the fillers, as shown in FIGS.
4A to 4E, is not only a hard magnetic substance only in Example 1
(FIG. 4A), but also a hard magnetic substance/a nonmagnetic
substance (FIG. 4B), a hard magnetic substance/a soft magnetic
substance (FIG. 4C), a hard magnetic substance/a nonmagnetic
substance/a soft magnetic substance (FIG. 4D), or a hard magnetic
substance/a soft magnetic substance/a nonmagnetic substance (FIG.
4E). Referring to FIG. 4A to 4E, the hard magnetic substance is
indicated by 41, the base electrode layer by 42, the substrate by
43, the nonmagnetic substance portion by 44, and the soft magnetic
substance portion by 45.
[0075] First, as shown in Example 1, the alumina nanoholes were
prepared, and the electrodeposition was performed in cases that a
nonmagnetic substance layer and a soft magnetic substance layer
were formed independently or stacked together.
[0076] Cu was adopted as the nonmagnetic substance, and with using
an aqueous solution that consists of copper sulfate (II)
pentahydrate, sulfuric acid, and thio uric acid, the
electrodeposition was performed at 24.degree. C. with applying a
voltage of -0.5 V to the Ag/AgCl reference electrode.
[0077] NiFe was adopted as the soft magnetic substance, and with
mixing nickel sulfate (II) heptahydrate with ferrous sulfate (II)
heptahydrate in a 1:1 ratio, the electrodeposition was similarly
performed at 24.degree. C. with applying a voltage of -1.0 V to the
Ag/AgCl reference electrode.
[0078] In addition, samples that are formed by stacking two kinds
of layers, that is, samples consisting of a nonmagnetic substance/a
soft magnetic substance, and a soft magnetic substance/a
nonmagnetic substance respectively were produced in separate baths
under the above described conditions.
[0079] In addition, it becomes possible to stack layers without
changing an electrodeposition liquid by performing the
electrodeposition with applying -0.5 V to the Ag/AgCl reference
electrode for the nonmagnetic substance layer and applying -1.0 V
for the soft magnetic substance layer in a mixed bath where an
electrodeposition liquid of Cu is mixed with an electrodeposition
liquid of NiFe in a 1:10 ratio. However, it cannot be avoided that
a small amount of another component is mixed.
[0080] The result of X-ray diffraction of the samples described
above is shown in Table 2. When Cu and NiFe were intermingled, the
diffraction intensity ratio of a material near a sample surface was
computed.
2 TABLE 2 Comparative Comparative Cu/NiFe NiFe/CU example example
for Mixed Mixed for Cu NiFe Cu only NiFe only Cu/NiFe NiFe/Cu bath
bath Applied voltage -2.0 V -3.1 V -0.5 V -1.0 V (vs Ag/AgCl) X-ray
diffraction 2.4 2.3 1.0 2.1 1.2 1.9 1.3 2.2 intensity ratio
(002)/(202) X-ray diffraction 6.4 4.5 911 680 865 713 844 685
intensity ratio (111)/(202)
[0081] Here, the Cu and NiFe comparative examples were samples at
the time of applying the above-described voltages, and it is
conceivable that the samples are approximately powder.
[0082] From the above, it was verified that both Cu and NiFe have
the fcc structure and their (111) faces are oriented in the
direction perpendicular to the substrate. In addition, when layers
were stacked, the tendency of the orientation did not change
regardless of the sequence to be good. Also in the
electrodeposition in the mixed bath of the nonmagnetic substance
and soft magnetic substance, it was verified that the (111) face
was oriented in the direction perpendicular to the substrate. It is
possible to estimate the orientation at about 98.5% in the sample
where only Cu is electrodeposited.
[0083] Furthermore, the result of X-ray diffraction at the time of
adding Co, which is a hard magnetic substance, to the last layer on
the conditions obtained above is shown in Table 3. The conditions
under which the c-axis was mostly orientated in Example 1 were used
as electrodeposition conditions of Co.
3 TABLE 3 Comparative Cu/NiFe NiFe/Cu example for Co Cu only NiFe
only Cu/NiFe NiFe/Cu mixed bath mixed bath Applied voltage -1.0 V
-1.0 V -1.0 V -1.0 V -1.0 V -1.0 V -1.0 V (vs Ag/AgCl) X-ray
diffraction 5.31 53.1 42.0 46.2 44.3 47.0 41.6 intensity ratio
(002)/(101) X-ray diffraction 0.73 0.80 0.84 0.76 0.77 0.79 0.81
intensity ratio (100)/(101)
[0084] Here, a Co comparative example expresses an example where
the c-axis was mostly oriented in Example 1.
[0085] As described above, in the structure of the fillers, it was
verified that a nonmagnetic substance and soft magnetic substance
layer had large influence also on the c-axis orientation of a hard
magnetic substance layer. Probably, it is expected that Cu (111)
face of the base electrode layer is oxidized in part after anodic
oxidation. Hence it is conceivable that the orientation in a
following layer was improved by covering this face with a material
having the same crystal structure.
Example 4
[0086] This example relates to a soft magnetic layer configured
under a base electrode layer.
[0087] First, a NiFe soft magnetic layer was formed at the
thickness of 1 .mu.m to 10 .mu.m on a Si substrate by sputtering.
Then, when surface roughness is observed by AFM (Atomic Force
Microscope), planarity becomes better as a thickness becomes
thinner. However, it is preferable from a role of a backing layer
of a recording medium that the film thickness is from 2 .mu.m to 5
.mu.m.
[0088] After formation of the NiFe layer, the Cu base electrode was
formed, and it verified from X-ray diffraction that the (111) face
was oriented in the direction perpendicular to the substrate.
Furthermore, in regard to the cases that the thickness of the NiFe
layer is 2 .mu.m, 3 .mu.m, and 5 .mu.m, anodic oxidation was
performed at 16.degree. C. in an oxalic acid bath with applying 40
V after formation of the aluminum film. When its cross sections
were observed by FE-SEM (field emission type scanning electron
microscope), the bottom of the nanoholes was uniform like the case
where there were no NiFe layers.
[0089] From the above, it is possible to insert the NiFe soft
magnetic substance layer under the base electrode layer.
Example 5
[0090] This example relates to MFM (magnetic force microscope)
observation of a hard magnetic substance, Co having hcp
structure.
[0091] First, Co, where the c-axis of 96.4% of Co was oriented in
Example 3, and the alumina nanoholes where the c-axes were evenly
distributed in Example 1 are prepared. At this time, a nanohole
diameter 53 was 50 nm and a nanohole interval 54 was 100 nm, and
the nanoholes were arranged regularly in a honeycomb shape as shown
in the plan of FIG. 5A. Each of FIG. 5B and 5C means a section
taken on line 5B-5B in FIG. 5A. Referring FIGS. 5A to 5C, a
recording portion is indicated by 51, and a portion comprised of
alumina by 52. It was verified that the pillar-like fillers that
were perpendicular to the substrate and consisted of Co were
uniformly formed according to the shape observation of their top
faces and cross sections with a FE-SEM.
[0092] Magnetization measurement was performed for the above
samples in 27.degree. C. in a range of -5000 (Oe) to 5000 (Oe).
Consequently, remanence ratios (Mr/Ms) of magnetized hysteresis
curves in the direction perpendicular to the substrate were 0.96
and 0.83 respectively, and the sample in which the c-axes of Co
were oriented showed a better value.
[0093] Furthermore, the observation of these was performed with an
MFM.
[0094] First, according to the observation after aligning the
direction of magnetization by applying a magnetic field of 3000
(Oe) in one direction, in the case of the sample in which Co was
oriented along the c-axis, an image showing that all fillers were
magnetized in the same direction was obtained as shown in FIG. 5C.
Conversely, in the case of the sample over which directions of the
c-axes were distributed uniformly, an image where the direction of
magnetization was inverted in about 12% of observation range (10
.mu.m.sup.2 range) was observed as shown in FIG. 5B.
[0095] Furthermore, writing was performed in the sample where the
c-axes of Co were oriented by applying 800 (Oe) of magnetic field
intermittently in a reverse direction in a state that magnetization
was aligned in one direction and scanning the sample at fixed
velocity with an MFM probe having high permeability. Consequently,
it was verified that the magnetization of only the portion,
corresponding to the time when the magnetic field was applied, from
among the range which the MFM probe scanned was inverted. At this
time, it was possible to perform recording in each nanohole of the
sample with a nanohole interval of 100 nm. In addition, in the
range of 10 .mu.m.sup.2, a record pattern was not changed even
after 10 hours exposure in 26.degree. C. Thus, since it is possible
to perform writing in each nanohole, this can be used as a
patterned medium.
[0096] Finally, writing was performed in the sample with a nanohole
interval of 35 nm similarly to the above. Consequently, it was
found that writing in each nanohole was unsuccessful since the MFM
probe was much large, but writing was performed in about six to
eight nanoholes at a time as a group in result of calculation from
the range of the image obtained. Thereby, it was verified that it
was also possible in writing to perform recording in a plurality of
nanoholes unlike the above-described recording in each nanohole. In
this case, it was also verified that it was not necessary that the
nanoholes were arranged regularly.
[0097] Thus, it was verified that, by orienting the c-axes of Co,
not only shape but also magneto crystalline anisotropy can be used
effectively, and that it is possible to suppress the inversion of
adjacent nanoholes in the hard magnetic substance due to
interaction, and stabilization thereof. Furthermore, it was also
verified to retain record.
Example 6
[0098] This example relates to S/N characteristics in a magnetic
record and reproduction output, and the like. This was performed
with using a magnetic recording apparatus having the structure as
roughly shown in FIG. 7.
[0099] A single magnetic pole head having the recording track width
of 1.0 .mu.m and the main pole thickness of 0.12 .mu.m was used for
recording on a perpendicular magnetic recording medium. An MR head
with the recording track width of 0.2 .mu.m was used for
reproduction of a signal. In addition, the head flying height at
the time of record and reproduction was set to be about 15 nm, and
the record and reproduction characteristic of the medium were
measured.
[0100] Samples prepared for measurement were a sample where 96.4%
of c-axes of Co hard magnetic substance in the nanoholes shown in
Example 3 were oriented (sample X), a sample where directions of
the c-axes in Example 1 were distributed uniformly (sample Y), and
also a sample where the c-axes were oriented and 3 .mu.m of NiFe
layer was formed as a backing layer 65 (FIG. 6B) under the base
electrode (sample Z). In addition, as shown in FIGS. 6A and 6B, a
nanohole diameter is 20 nm, and a nanohole interval is about 35 nm.
FIG. 6B means a section taken on line 6B-6B in FIG. 6A. Referring
FIGS. 6A and 6B, a recording portion is indicated by 61, a portion
comprised of alumina by 62, a region of one bit by 63, a base
electrode layer by 64, and a substrate by 66.
[0101] The measurement result of these samples is summarized in
Table 4. C-axis orientation was computed from the comparison with
X-ray diffraction intensity ratio of a powder sample.
4 TABLE 4 Sample X Sample Y Sample Z c-axis orientation degree
96.4% 83.4% 92.3% NiFe backing layer No No Yes S/N relative value
2.21 1.00 1.95 Error rate 1.0 .times. 10.sup.-8 1.0 .times.
10.sup.-5 4.0 .times. 10.sup.-9
[0102] Thus, in record to and reproduction from the hard magnetic
substance where the c-axes in the regular nanoholes are oriented,
the volume, shape, and magneto crystalline anisotropy of hard
magnetic substances of respective nanoholes that serve as recording
portions in FIG. 6A are uniform. Hence noise is very low, and
therefore, an S/N relative value is good. In addition, it was
verified that, although a noise level slightly increased owing to
formation of the backing layer, the S/N relative value was good and
there was no problem of rewriting adjacent portions at the time of
recording. A medium having such a small nanohole diameter and a
small nanohole interval can perform perpendicular recording as one
bit in a plurality of nanoholes as shown in FIGS. 6A and 6B. Hence
this demonstrates the possibility as a future perpendicular
magnetic recording apparatus.
Example 7
[0103] Samples were prepared, the sample each of which separately
has a 10 nm-thick Pt, Pd, Cu, Ir, or Rh film on an MgO substrate by
a sputter vacuum deposition. Then, an aluminum film of 500 nm thick
was formed on all the samples. Furthermore, anodic oxidation was
performed at 16.degree. C. in 0.3 M of oxalic acid aqueous solution
with applying 40 V of voltage. Next, the substrates were dipped for
25 minutes in 0.5wt% of phosphoric acid aqueous solution for
expanding hole diameters. At this time, the Pt, Pd, Cu, Ir, and Rh.
films were oriented respectively to the (001) face to the direction
perpendicular to the substrate. Hence, in each nanohole bottom, the
Pt, Pd, Cu, Ir, or Rh surface was exposed to make conductivity
good.
[0104] Thus, the nanoholes of the sample whose conductive layer was
Pt, as a typical example, was filled with CoPt, which is a hard
magnetic substance. Here, the composition of an aqueous solution
used at 24.degree. C. for the electrodeposition of CoPt was
hydrogen hexachloroplatinate(IV) 6-hydrate solution of 0.003 mol/l,
cobalt sulfate (II) heptahydrate 0.3 mol/l, boric acid of 30 g/l,
and magnesium sulfate heptahydrate of 50 g/l.
[0105] The electrodeposition was performed in the above-described
solution with using Ag/AgCl as a reference electrode in each case
of -1.5 V, -0.8 V, and -0.6 V.
[0106] Furthermore, the electrodeposited materials that overflowed
on the surface were ground and removed from these samples with
using the diamond slurry of 1/4 .mu.m. At this time, surface Rms
was 1 nm or less.
[0107] When the above samples were observed with a field emission
type scanning electron microscope (FE-SEM), the fillers exist in
all nanoholes. It was verified that the linearity of nanoholes was
also excellent through the observation from cross sections.
[0108] The result of performing component analysis with these ICPs
is shown in Table 5. This composition includes also Pt of the
electrode layer. In this case, it is sufficient for this
composition to include an electrode layer for becoming spread and
uniform after heat treatment.
5 TABLE 5 -0.6 V -0.8 V -1.5 V Co composition 0.06 0.52 0.95 Pt
composition 0.94 0.48 0.05
[0109] From the above, the composition of Co was low in the sample
electrodeposited at -0.6 V. In addition, the composition of Co was
large enough in the sample electrodeposited at -1.5 V, which was
greatly shifted from the composition of CoPt with the L1.sub.0
ordered structure. In the sample at -0.8 V, the diffraction of
fcc:CoPt (002) was mainly observed.
[0110] X-ray diffractometry of the sample electrodeposited at -0.8
V was performed again after sufficient annealing in a 650.degree.
C. reducing atmosphere. Then, a peak of CoPt (002) with the
L1.sub.0 ordered structure could be observed in the sample
electrodeposited at -0.8 V. With calibrating this by the
diffraction intensity ratio of the powder sample listed in JCPDS,
78% of the whole c-axes were oriented in the direction
perpendicular to the substrate, and the remainders were in other
directions. In addition, CoPt (111) with the L1.sub.0 ordered
structure appears preferentially when the electrode layer is a Pt
(111) face. Hence, it can be verified that the c-axes of CoPt with
the L1.sub.0 ordered structure are oriented preferentially in the
direction perpendicular to the substrate by making the electrode
layer a Pt (001) face.
Example 8
[0111] In this example, the measurement similar to that of Example
7 in the case where an electrode layer has ordered structure.
[0112] First, samples prepared were those where a 10 nm-thick CoPt
film with L1.sub.0 ordered structure, a 10 nm-thick CuPt film with
L1i ordered structure, or a 10 nm-thick CoPt.sub.3 with L1.sub.2
ordered structure were formed on each MgO substrate. After that, an
Al film of 500 nm thick was formed on each sample.
[0113] These three samples were anodized under the same conditions
as those in Example 7. It was verified that similarly to the Pt
electrode layer, since a square array face was oriented in the
direction perpendicular to the substrate, and hence conductivity
was good since a face of each conductive layer was exposed in the
bottom of a nanohole. In particular, it was verified that the
c-axes were oriented in the direction perpendicular to the
substrate in the case of the L1.sub.0 ordered structure.
[0114] As described above, the nanoholes was filled with CoPt,
which is a hard magnetic substance, if the conductive layer has the
L1.sub.0 ordered structure. Here, the composition of an aqueous
solution used at 24.degree. C. for the electrodeposition of CoPt
was hydrogen hexachloroplatinate(IV) 6-hydrate solution of 0.003
mol/l, cobalt sulfate (II) heptahydrate 0.3 mol/l, boric acid of 30
g/l, and magnesium sulfate heptahydrate of 50 g/l.
[0115] The electrodeposition was performed at -0.8 V in the above
solution with using Ag/AgCl as a reference electrode. Although the
Co composition became larger than the composition in Example 7
because Co was included in the electrode layer, Co was few enough
in comparison with an amount of electrodeposition. Hence there was
hardly shifted on composition, and this was the composition of
forming CoPt with the L1.sub.0 ordered structure. Furthermore, the
electrodeposited materials that overflowed on the surface were
ground and removed from these samples with using the diamond slurry
of 1/4 .mu.m. At this time, surface Rms was 1 nm or less.
[0116] In result of X-ray diffraction measurement, a peak of
fcc-CoPt (002) was mainly observed. X-ray diffractometry of these
samples was performed again after sufficient annealing in a
650.degree. C. reducing atmosphere. Then, a peak of CoPt (002) with
the L1.sub.0 ordered structure was observed. With calibrating this
by the diffraction intensity ratio of the powder sample listed in
JCPDS, 84% of the whole c-axes were oriented in the direction
perpendicular to the substrate.
[0117] Hence, it can be verified that the c-axes of CoPt with the
L1.sub.0 ordered structure are oriented preferentially in the
direction perpendicular to the substrate also when CoPt with the
L1.sub.0 ordered structure is used as the electrode layer.
Example 9
[0118] This example relates to a manufacturing method and
orientation of a nonmagnetic substance and soft magnetic substance
portions in the structure of fillers, and the orientation of a hard
magnetic substance portion caused by the result.
[0119] First, possible structure of the fillers, as shown in FIGS.
4A to 4E, is not only a hard magnetic substance only in Example 7
(FIG. 4A), a hard magnetic substance/a nonmagnetic substance (FIG.
4B), a hard magnetic substance/a soft magnetic substance (FIG. 4C),
a hard magnetic substance/a nonmagnetic substance/a soft magnetic
substance (FIG. 4D), or a hard magnetic substance/a soft magnetic
substance/a nonmagnetic substance (FIG. 4E).
[0120] First, five types of alumina nanoholes which adopted Pt, Pd,
Cu, Ir, and Rh as respective conductive layers were prepared as
shown in Example 7. The electrodeposition was performed in cases
that a nonmagnetic substance layer and a soft magnetic substance
layer were formed independently or stacked together. Consequently,
it was verified that the orientation after the electrodeposition
was kept as the conductive layer was, and the layer was oriented to
the (001) face.
[0121] In particular, in this example, the case that a conductive
layer is Pt will be described in detail.
[0122] First, so as to perform electrodeposition of Pt as the
nonmagnetic substance, with using an aqueous solution of 0.03 mol/l
that consists of platinum chloride hexahydrate, the
electrodeposition was performed at 24.degree. C. with applying a
voltage of -0.5 V to the Ag/AgCl reference electrode.
[0123] NiFe was adopted as the soft magnetic substance, and with
mixing nickel sulfate (II) heptahydrate with ferrous sulfate (II)
heptahydrate in a 1:1 ratio, the electrodeposition was similarly
performed at 24.degree. C. with applying a voltage of -1.0 V to the
Ag/AgCl reference electrode.
[0124] In addition, samples-that are formed by stacking two kinds
of layers, that is, samples consisting of a nonmagnetic substance/a
soft magnetic substance, and a soft magnetic substance/a
nonmagnetic substance respectively were produced in separate
baths.
[0125] In addition, it becomes possible to perform stacking without
changing the electrodeposition liquid with applying -0.5 V to the
Ag/AgCl reference electrode for the nonmagnetic substance layer,
and with applying -1.0 V for the soft magnetic layer in a mixed
bath where the above-described electrodeposition liquid of Pt and
NiFe was mixed in a 1:10 ratio. However, it cannot be avoided that
a small amount of another component is mixed.
[0126] According to the result of X-ray diffraction of the above
samples, the single Pt layer was most oriented to the fcc (001)
face in the direction perpendicular to the substrate most. Hence it
can be verified that 94% of Pt is oriented with calibrating it with
diffraction intensity from the powder sample listed in JCPDS. In
addition, it can be verified that 80% or more of the whole magnetic
substance is oriented to the fcc (001) to the direction
perpendicular to the substrate in every sample which is combined,
especially is given the electrodeposition in the mixed bath.
[0127] Furthermore, the result of X-ray diffraction at the time of
adding CoPt, which is a hard magnetic substance, to the last layer
under the conditions obtained above is shown in Table 3. The
electrodeposition conditions of CoPt are -0.8 V at which maximum
orientation was obtained in Examples 7 and 8, and after that, the
samples were heated at 650.degree. C. for 2 minutes in an RTA. This
is for suppressing counter diffusion with the non-magnetic or soft
magnetic layer.
[0128] The ratio of the above result when setting a comparative
example to 1 with making the degree of the orientation of CoPt with
the L1.sub.0 ordered structure to the (002) face in Example 7 as
the Comparative Example is shown in Table 6.
6TABLE 6 Pt/NiFe NiFe/Pt Comparative NiFe mixed mixed example Pt
only only Pt/NiFe NiFe/Pt bath bath 1 1.18 1.11 1.05 1.06 1.02
1.02
[0129] Thus, in the structure of the fillers, it was verified that
a nonmagnetic substance and soft magnetic substance layer had
influence also on the c-axis orientation of a hard magnetic
substance layer. Probably, it is expected that Pt (001) face of the
conductive layer is oxidized in part after anodic oxidation. Hence
it is conceivable that the orientation in a following layer was
improved by covering this face with a material having the same
crystal structure. In addition, the same effect can be also
obtained in other conductive layers.
Example 10
[0130] This example relates to a soft magnetic layer configured
under a conductive layer.
[0131] A Pt electrode layer was formed after forming a NiFe layer
on an MgO (001) face. Then, it could be verified from X-ray
diffraction that the (001) face of a Pt electrode layer was
oriented in the direction perpendicular to the substrate.
Furthermore, anodic oxidation was performed at 16.degree. C. in an
oxalic acid bath with applying a voltage of 40 V after further
forming a NiFe layer of 2 .mu.m thick and forming an Al film. Then,
when its cross sections were observed by FE-SEM (field emission
type scanning electron microscope), the bottoms of the nanoholes
were uniform like the case where there were no NiFe layers.
[0132] Moreover, Pt electrodeposition was performed and recording
was performed by contacting a magnetic head after CoPt formation
with the L1.sub.0 ordered structure. At this time, with comparing
the result with the sample not having the soft magnetic layer under
the conductive layer, intensity of magnetic field for recording was
0.76 times. Hence it could be verified that magnetic flux
concentration was promoted by the soft magnetic layer.
[0133] From the above, it is effective to intercalate a NiFe soft
magnetic substance layer under a conductive layer.
Example 11
[0134] This example relates to MFM (Magnetic Force Microscope)
observation of a hard magnetic substance, CoPt having L1.sub.0
ordered structure.
[0135] First, a Pt electrodeposition step was performed in
condition of Example 9. Thus, alumina nanoholes filled with CoPt
with the L1.sub.0 ordered structure, which was oriented 1.18 times
as many as the comparative example, and CoPt with the L1.sub.0
ordered structure, where the c-axes were uniformly distributed over
all directions, were prepared. At this time, a nanohole diameter
was 50 nm and a nanohole interval was 100 nm, and the nanoholes
were arranged regularly in a honeycomb shape as shown in the plan
of FIG. 5A. It was verified that the pillar-like fillers that were
perpendicular to the substrate and consisted of CoPt with the
L1.sub.0 ordered structure were uniformly formed according to the
shape observation of their top faces and cross sections with a
field emission type scanning electron microscope (FE-SEM).
[0136] Magnetization measurement was performed for the above
samples in 27.degree. C. in a range of -25000 (Oe) to 25000 (Oe).
Consequently, remanence ratios (Mr/Ms) of magnetized hysteresis
curves in the direction perpendicular to the substrate were 0.91
and 0.74 respectively, and the sample in which the c-axes of CoPt
with the L1.sub.0 ordered structure were oriented showed a better
value.
[0137] Furthermore, the observation of these was performed with an
MFM.
[0138] First, the samples were observed after applying the magnetic
field of 25000 (Oe) in one direction and sufficiently aligning the
direction of magnetization. Then, from the sample in which the
c-axes of CoPt with the L1.sub.0 ordered structure were oriented,
an image showing that all fillers were oriented in the same
direction as shown in FIG. 5C was obtained. When observing again
two days after, the direction of magnetization was kept in all
fillers. Conversely, it was conceivable that the sample where the
c-axes were distributed uniformly was in a magnetization state as
shown in FIG. 5B. Owing to the magnetic coupling with adjacent
magnetized fillers, a leakage magnetic field was weak, measurement
was difficult, and magnetic contrast was hardly obtained. This is
conceivable that the c-axes were also oriented in the direction
parallel to the substrate's surface, and hence, the magnetic field
was closed inside over the whole film.
[0139] In addition, with observing the sample after applying the
magnetic field of 25000 (Oe) in the opposite direction to reverse
the direction of magnetization, an image with a contrast contrary
to the image previously observed was obtained. Hence, in the film
of CoPt with the L1.sub.0 ordered structure where the c-axes were
oriented in the direction perpendicular to the substrate, it can be
verified the possibility as a perpendicular magnetic medium.
However, it is also possible to lower the intensity of the magnetic
field required for magnetization reversal by mixing a minute amount
of another element.
[0140] Thus, it was verified that, by orienting the c-axes of CoPt
with the L1.sub.0 ordered structure, not only shape but also
magneto crystalline anisotropy can be used effectively, and that it
is possible to suppress the inversion of adjacent nanoholes in the
hard magnetic substance due to interaction, and stabilization
thereof. Furthermore, it was also verified to retain record.
Example 12
[0141] In this example, a magnetic recording apparatus configures
as roughly shown in FIG. 7 can be configured.
[0142] As attempted in Example 11, in the recording medium
according to the present invention, it is possible to align the
magnetizing direction of fillers by applying a magnetic field, and
also to retain information. Hence, it is also possible to record
information of one bit by the magnetizing direction of countless
fillers by sufficiently reducing each size of fillers to 10 nm or
less. Alternatively, although the size is about 25 nm, it is also
possible to record information of one bit on single filler. Then,
it is possible to form a magnetic recording apparatus by assembling
a recording medium according to the present invention, a magnetic
recording medium driving unit, a magnetic head, a magnetic head
driving unit, and a signal processing unit, into an apparatus as
shown in FIG. 7. However, according to this example, the driving of
a magnetic recording medium is not limited to only the rotation and
the driving of a magnetic head is not limited to only the slide on
a periphery.
* * * * *