U.S. patent application number 12/397786 was filed with the patent office on 2009-10-15 for smco-based alloy nanoparticles and process for their production.
This patent application is currently assigned to TDK Corporation. Invention is credited to Haruki Kinjo, Mutsuko Kinjo, Mamoru Satoh, Shiho Tokonami, Naoki Toshima.
Application Number | 20090257907 12/397786 |
Document ID | / |
Family ID | 41164156 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090257907 |
Kind Code |
A1 |
Satoh; Mamoru ; et
al. |
October 15, 2009 |
SmCo-BASED ALLOY NANOPARTICLES AND PROCESS FOR THEIR PRODUCTION
Abstract
SmCo-based alloy nanoparticles composed mainly of a SmCo-based
alloy containing Sm and Co as constituent elements, wherein the
content of metal elements other than Sm and Co is 0.05-20 wt % with
respect to the SmCo-based alloy.
Inventors: |
Satoh; Mamoru; (Tokyo,
JP) ; Toshima; Naoki; (Tokyo, JP) ; Kinjo;
Mutsuko; (SanyoOnoda-shi, JP) ; Kinjo; Haruki;
(Ginowann-shi, JP) ; Tokonami; Shiho;
(SanyoOnoda-shi, JP) |
Correspondence
Address: |
DRINKER BIDDLE & REATH (DC)
1500 K STREET, N.W., SUITE 1100
WASHINGTON
DC
20005-1209
US
|
Assignee: |
TDK Corporation
Chuo-ku
JP
Tokyo University of Science Educational Foundation
Administrative Organization
Shinjuku-ku
JP
|
Family ID: |
41164156 |
Appl. No.: |
12/397786 |
Filed: |
March 4, 2009 |
Current U.S.
Class: |
420/416 ;
420/435; 420/580; 75/351 |
Current CPC
Class: |
B22F 2999/00 20130101;
B82Y 30/00 20130101; C30B 29/52 20130101; B22F 1/0018 20130101;
C22C 28/00 20130101; H01F 1/0553 20130101; H01F 1/0552 20130101;
C30B 29/60 20130101; C30B 7/14 20130101; H01F 1/0551 20130101; B22F
9/24 20130101; B22F 2999/00 20130101; B22F 1/0018 20130101; B22F
2207/07 20130101 |
Class at
Publication: |
420/416 ;
420/435; 420/580; 75/351 |
International
Class: |
C22C 28/00 20060101
C22C028/00; C22C 19/07 20060101 C22C019/07; C22C 30/00 20060101
C22C030/00; B22F 9/18 20060101 B22F009/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2008 |
JP |
P2008-058346 |
Claims
1. SmCo-based alloy nanoparticles composed mainly of a SmCo-based
alloy containing Sm and Co as constituent elements, wherein the
content of metal elements other than Sm and Co is 0.05-20 wt % with
respect to the SmCo-based alloy.
2. SmCo-based alloy nanoparticles according to claim 1, wherein the
content of the metal elements is 0.05-10 wt % with respect to the
SmCo-based alloy.
3. SmCo-based alloy nanoparticles according to claim 1, wherein the
metal elements include at least one element selected from the group
consisting of Au, Ag, Pt, Pd, Rh, Ru, Ir, Os, Cu, Ni, Cr, Al and
Mn.
4. SmCo-based alloy nanoparticles according to claim 1, wherein the
particle sizes are 1-30 nm.
5. SmCo-based alloy nanoparticles according to claim 1, which are
obtained by liquid synthesis wherein a strong reducing agent is
added to an organic solvent containing a samarium salt, a cobalt
salt and metal element salts, to reduce the samarium salt, the
cobalt salt and the metal element salts.
6. SmCo-based alloy nanoparticles according to claim 1, having a
core-shell structure comprising a core section and a shell section
covering the core section, wherein the proportion of the metal
elements with respect to the SmCo-based alloy in the core section
is greater than the proportion in the shell section.
7. A process for production of SmCo-based alloy nanoparticles
composed mainly of a SmCo-based alloy containing Sm and Co as
constituent elements, the process comprising: a mixing step in
which a starting material containing a samarium salt, a cobalt salt
and salts of metal elements other than Sm and Co, as well as a
protective agent, is mixed with a reducing organic solvent; and a
reduction step in which a strong reducing agent is added to the
mixture and heated to reduce the samarium salt, the cobalt salt and
the salts of the metal elements.
8. A process for production of SmCo-based alloy nanoparticles
according to claim 7, further comprising a dehydration step in
which the mixture obtained from the mixing step is stirred and
heated for uniform dissolution and dehydration and then cooled,
prior to the reduction step.
9. A process for production of SmCo-based alloy nanoparticles
according to claim 7, wherein the metal elements include at least
one element selected from the group consisting of Au, Ag, Pt. Pd,
Rh, Ru, Ir, Os, Cu, Ni, Cr, Al and Mn.
10. A process for production of SmCo-based alloy nanoparticles
according to claim 7, wherein the strong reducing agent contains at
least one compound selected from the group consisting of
LiAlH.sub.4, NaBH.sub.1, N.sub.2H.sub.4, B.sub.2H.sub.6 and
LiBH(C.sub.2H.sub.5).sub.3.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to SmCo-based alloy
nanoparticles and to a process for their production.
[0003] 2. Related Background Art
[0004] A large variety of magnetic materials are used in the fields
of magnetic recording media and magnets. SmCo-based alloy magnetic
materials have very high coercive force and uniaxial
magnetocrystalline anisotropy, and are known to exhibit high
magnetic properties even as nanoparticles. SmCo-based alloys,
therefore, are promising materials for use as various types of
magnetic materials, including magnetic recording media for
high-density recording.
[0005] Methods for synthesis of SmCo-based alloy particles are
known which allow synthesis of SmCo.sub.5 alloy particles by the
physical method of sputtering (for example, see Reference 1 listed
below). Another method that has been proposed is vapor phase
deposition with a cluster gun to produce SmCo-based alloy particles
(for example, see Reference 2 listed below).
(Reference 1) D. Weller, et al, IEEE Trans. Magn, 36, p. 10-15
(2000) (Reference 2) S. Stoyanov et al., "High anisotropy Sm--Co
nanoparticles: Preparation by cluster gun technique and their
magnetic properties", JOURNAL OF APPLIED PHYSICS, Vol 93, Number 10
(2003), p. 7592
[0006] On the other hand, methods for synthesizing SmCo-based alloy
particles by chemical means have also been proposed, such as
synthesis by polyol reduction (see Japanese Unexamined Patent
Publication No. 2006-245313, for example) and synthesis by
microwave polyol reduction (see Japanese Unexamined Patent
Publication No. 2007-128991, for example).
SUMMARY OF THE INVENTION
[0007] However, research by the present inventors has revealed that
SmCo-based particles obtained by physical synthesis as in
References 1 and 2 do not have very high magnetic properties. Then,
such physical synthesis require heat treatment and have low
SmCo-based particle yields, they are unsuitable for industrial mass
production.
[0008] On the other hand, the SmCo-based alloy particles disclosed
in Japanese Patent Laid-Open No. 2006-245313 have a coercive force
(Hc) of as low as 500 Oe at ordinary temperature. Also, the
SmCo-based alloy nanoparticles disclosed in Japanese Patent
Laid-Open No. 2007-128991 have only been observed to exhibit
magnetic properties at cryogenic temperature. The low magnetic
properties of the SmCo-based alloy particles disclosed in the
aforementioned patent documents are attributed to the fact that the
SmCo-based alloy particles that are produced contain large amounts
of unreacted samarium salts, since samarium salts are not easily
reduced substances.
[0009] SmCo-based particles have therefore been desired which
exhibit satisfactorily excellent magnetic properties and have
sufficiently small particle sizes. A process for production
allowing such SmCo-based alloy nanoparticles to be easily produced
in mass has also been desired.
[0010] It is an object of the present invention to provide
SmCo-based alloy nanoparticles with sufficiently small particle
sizes and satisfactorily excellent magnetic properties, as well as
a production process that allows the SmCo-based alloy nanoparticles
to be mass-produced at high yield.
[0011] In order to achieve this object, the invention provides
SmCo-based alloy nanoparticles composed mainly of a SmCo-based
alloy containing Sm and Co as constituent elements, wherein the
content of metal elements other than Sm and Co is 0.05-20 wt % with
respect to the SmCo-based alloy.
[0012] Such SmCo-based alloy nanoparticles can be suitably used as
magnetic material because of their sufficiently small particle
sizes and satisfactorily excellent magnetic properties. The reason
for the satisfactorily excellent magnetic properties of the
SmCo-based alloy nanoparticles of the invention is that they have
sufficiently low unreacted components and comprise a SmCo-based
alloy as the major component. By varying the content of the metal
elements other than Sm and Co, it is possible to control the
magnetic properties and particle sizes of the SmCo-based alloy
nanoparticles of the invention, and to improve the degree of design
freedom for magnets or magnetic recording media.
[0013] The SmCo-based alloy nanoparticles of the invention
preferably contain the aforementioned metal elements at 0.05-10 wt
% with respect to the SmCo-based alloy. SmCo-based alloy
nanoparticles with this range exhibit even more excellent magnetic
properties.
[0014] The metal elements in the SmCo-based alloy nanoparticles of
the invention preferably include at least one element selected from
the group consisting of Au, Ag, Pt, Pd, Rh, Ru, Ir, Os, Cu, Ni, Cr,
Al and Mn. SmCo-based alloy nanoparticles comprising these metal
elements as the metal elements exhibit even more superior magnetic
properties.
[0015] The SmCo-based alloy nanoparticles of the invention
preferably have particle sizes of 1-30 nm. SmCo-based alloy
nanoparticles in this range can be suitably used as magnetic
recording media for high-density recording, for example.
[0016] The SmCo-based alloy nanoparticles of the invention are
preferably obtained by liquid synthesis wherein a strong reducing
agent is added to an organic solvent containing a samarium salt,
cobalt salt and metal element salts, to reduce the samarium salt,
cobalt salt and metal element salts. Such SmCo-based alloy
nanoparticles are particularly useful in industry as starting
materials for magnetic materials, because of their excellent mass
productivity and relatively high particle size distribution.
[0017] The SmCo-based alloy nanoparticles of the invention have a
core-shell structure comprising a core section and a shell section
covering the core section, and preferably the proportion of the
metal elements with respect to the SmCo-based alloy in the core
section is greater than the proportion in the shell section.
[0018] According to the invention there is further provided a
process for production of SmCo-based alloy nanoparticles composed
mainly of a SmCo-based alloy containing Sm and Co as constituent
elements, the process comprising a mixing step in which a starting
material containing a samarium salt, cobalt salt and salts of metal
elements other than Sm and Co, as well as a protective agent, is
mixed with a reducing organic solvent, and a reduction step in
which a strong reducing agent is added to the mixture and heated to
reduce the samarium salt, cobalt salt and metal element salts.
[0019] By the process for production of SmCo-based alloy
nanoparticles described above it is possible to accomplish
high-yield production of SmCo-based alloy nanoparticles with
sufficiently small particle sizes and satisfactorily excellent
magnetic properties. The reason for this effect is conjectured by
the present inventors to be as follows. Specifically, it is
believed that reduction of samarium salts or cobalt salts results
in rapid reduction of the salts of the metal elements other than Sm
and Co in the starting material, while the metal elements exhibit a
catalytic effect whereby they serve as nuclei for crystal
deposition which promotes deposition of the SmCo-based alloy
crystals. This allows smooth synthesis of SmCo-based alloy
nanoparticles with a sufficiently reduced content of unreacted
substances. The catalytic effect of the metal elements adequately
shortens the reaction time and inhibits grain growth of the
produced SmCo-based alloy nanoparticles. It is therefore possible
to synthesize SmCo-based alloy nanoparticles that have
satisfactorily excellent magnetic properties and sufficiently small
particle sizes. Furthermore, since the production process of the
invention employs the chemical process of reduction of the starting
material to synthesize the SmCo-based alloy nanoparticles, it
allows mass production of SmCo-based alloy nanoparticles at a
higher yield than physical methods such as sputtering.
[0020] The production process of the invention preferably includes
a dehydration step in which the mixture obtained from the mixing
step is stirred and heated for dehydration and then cooled, prior
to the reduction step. This sufficiently removes moisture before
the reduction step, thus inhibiting oxidation of Sm and Co and
allowing the reduction reaction of the samarium salt and cobalt
salt to proceed even more smoothly. In addition, if the mixture is
cooled to near room temperature after dehydration and then a strong
reducing agent is added prior to further strength and heating, it
is possible to prevent the bumping that occurs when reduction
reaction proceeds at once, and to thus reduce impurities. That is,
by adding a strong reducing agent after cooling, SmCo-based alloy
nanoparticles with excellent magnetic properties can be produced at
high yield, having a further reduced unreacted substance content
and even lower content of impurities other than the SmCo-based
alloy.
[0021] According to the production process of the invention, the
metal elements preferably include at least one element selected
from the group consisting of Au, Ag, Pt, Pd, Rh, Ru, Ir, Os, Cu,
Ni, Cr, Al and Mn. Since these metal elements are more easily
reduced than samarium salts or cobalt salts, they become rapidly
reduced as crystal-generating nuclei, thus exhibiting a more
superior catalytic effect. Reduction of the samarium and cobalt
salts can therefore be further promoted.
[0022] The strong reducing agent used in the production process of
the invention preferably contains at least one compound selected
from the group consisting of LiAlH.sub.4, NaBH.sub.4, N.sub.2H,
B.sub.2H.sub.6 and LiBH(C.sub.2H.sub.5).sub.3. This will allow
SmCo-based alloy nanoparticles to be obtained with a further
reduced amount of residual unreacted samarium salt or cobalt
salt.
[0023] According to the invention it is possible to provide
SmCo-based alloy nanoparticles with sufficiently small particle
sizes and satisfactorily excellent magnetic properties, as well as
a production process that allows the SmCo-based alloy nanoparticles
to be mass-produced at high yield.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 shows a high-resolution TEM photograph and an
electron diffraction image of SmCo-based alloy nanoparticles
composed mainly of SmCo.sub.5, according to an embodiment of the
invention.
[0025] FIG. 2 is a field-emission transmission electron microscope
(FE-TEM) photograph showing an example of the microstructure of a
SmCo-based alloy nanoparticle according to the invention.
[0026] FIG. 3 is a scanning transmission electron microscope (STEM)
photograph of the SmCo-based alloy nanoparticle shown in FIG.
2.
[0027] FIG. 4 is an XRD chart showing the results of XRD analysis
of synthesized particles.
[0028] FIG. 5 is a graph showing the magnetic properties of the
SmCo.sub.5 nanoparticles of Example 2 described hereunder.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] A preferred embodiment of the invention will now be
explained with reference to the accompanying drawings where
necessary.
[0030] The SmCo-based alloy nanoparticles of this embodiment have a
mean particle size of 1-30 nm. Thus, since the SmCo-based alloy
nanoparticles with nanosize particle sizes have excellent magnetic
properties and sufficiently small particle sizes, they can be used
as magnetic powder for magnetic recording media, to increase the
recording density of the magnetic recording media. The particle
sizes of the SmCo-based alloy nanoparticles can be measured by
observation with a transmission electron microscope (TEM).
[0031] The preferred composition for the SmCo-based alloy as the
major component of the SmCo-based alloy nanoparticles is
SmCo.sub.5. FIG. 1(a) is a high-resolution TEM photograph of the
SmCo-based alloy nanoparticles composed mainly of SmCo.sub.5
according to this embodiment, and FIG. 1(b) is an electron
diffraction image of the SmCo-based alloy nanoparticles composed
mainly of SmCo.sub.5 according to this embodiment. The SmCo-based
alloy nanoparticles having this composition exhibit excellent
coercive force (Hc) and magnetization. The composition of the
SmCo-based alloy nanoparticles may be confirmed by ICP optical
emission spectroscopic analysis. Because SmCo.sub.5 has a
CaCu.sub.5-type crystal structure, it can also be identified by
X-ray diffraction (XRD).
[0032] The SmCo-based alloy nanoparticles of this embodiment are
composed mainly of a SmCo-based alloy, and contain a metal element
other than Sm and Co (hereinafter referred to as "third metal
element") at 0.05-20 wt % with respect to the total SmCo-based
alloy. The third metal element may be present in the SmCo-based
alloy nanoparticles as a simple metal or a metal compound.
[0033] The third metal element content is preferably 0.05-20 wt %
and more preferably 0.05-10 wt % with respect to the total
SmCo-based alloy. The third metal element content can be confirmed
by ICP optical emission spectroscopic analysis or the like.
[0034] If the third metal element content is less than 0.05 wt %
with respect to the obtained SmCo-based alloy nanoparticles during
production of the SmCo-based alloy nanoparticles, the improving
effect of the third metal element will not be adequately obtained
and the SmCo-based alloy nanoparticle yield will be reduced, while
the unreacted substance content will be increased, thus resulting
in inferior magnetic properties. If the third metal element content
is greater than 20 wt %, on the other hand, the lower proportion of
SmCo-based alloy contributing to the magnetic properties will
result in reduced magnetic properties.
[0035] The third metal element may be a precious metal element such
as Au, Ag, Pt, Pd, Rh, Ru, Ir or Os, or a transition metal element
such as Cu, Ni, Cr or Mn. Al may be mentioned as an example of a
third metal element other than these.
[0036] The SmCo-based alloy nanoparticles of this embodiment may
have a core-shell structure comprising a core section with the
third metal element as the major component, and a shell section
containing a SmCo-based alloy as the major component, covering the
periphery of the core section.
[0037] FIG. 2 is a field-emission transmission electron microscope
(FE-TEM: JEM-2010F, trade name of JEOL Corp.) photograph showing an
example of the microstructure of a SmCo-based alloy nanoparticle
according to the invention. As shown in FIG. 2, regions with
different contrasts are present in a single SmCo-based alloy
nanoparticle. The SmCo-based alloy nanoparticles are polycrystals,
and the interference pattern differs between the core section
(center section) and the shell section (outer shell section). Thus,
the SmCo-based alloy nanoparticle shown in FIG. 2 has a core-shell
structure comprising a core section and a shell section having
different compositions.
[0038] FIG. 3 is a scanning transmission electron microscope (STEM)
photograph of the SmCo-based alloy nanoparticle shown in FIG. 2.
Elemental analysis can be carried out using an energy dispersive
X-ray spectrometer (EDS: NORAN-UTW, trade name of NORAN). As shown
in FIG. 3, the SmCo-based alloy nanoparticles of this embodiment
contain the third metal element (Au) as the major component in the
core section of each SmCo-based alloy nanoparticle (region 1 in
FIG. 3), and the SmCo-based alloy as the major component in the
shell section (region 2 in FIG. 3).
[0039] A process for production of the SmCo-based alloy
nanoparticles of this embodiment will now be explained. The process
for production of SmCo-based alloy nanoparticles of this embodiment
comprises a preparation step in which the samarium salt, cobalt
salt and third metal element salt are each dissolved in a reducing
organic solvent to prepare solutions, a mixing step in which the
samarium salt solution, the cobalt salt solution and the third
metal element salt solution are mixed to obtain a mixture, an
addition step in which a protective agent is added to the mixture
obtained in the mixing step, a dehydration step in which the
mixture containing the protective agent is heated for dehydration,
and a reduction step in which a strong reducing agent is added to
the dehydrated mixture to reduce the samarium salt, cobalt salt and
third metal element salt, in order to obtain SmCo-based alloy
nanoparticles containing the third metal element. Each of these
steps will now be explained in detail.
[0040] (Preparation Step)
[0041] The Sm (samarium) salt used for this embodiment may be
samarium acetylacetonate hydrate
([CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.3Sm.xH.sub.2O), and the Co
(cobalt) salt may be cobalt acetylacetonate
([CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.3Co). These salts are
readily soluble in organic solvents and relatively easily reduced,
and are therefore preferably used from the viewpoint of obtaining
SmCo-based alloy nanoparticles with small particle sizes and high
purity.
[0042] The third metal element salt may be an acetylacetonate salt.
Acetylacetonate salts are preferred for use because they are
readily soluble in organic solvents.
[0043] The organic solvent used to dissolve the samarium salt,
cobalt salt and third metal element salt is preferably one with a
high boiling point. A specific example is 1,2-hexadecanediol, which
has reducing action.
[0044] Dissolution of the samarium salt, cobalt salt and third
metal element salt in 1,2-hexadecanediol in the preparation step
produces a solution containing the samarium salt, a solution
containing the cobalt salt and a solution containing the third
metal element salt. In order to prevent oxidation of the Sm, Co and
third metal element, the preparation step is preferably carried out
in an inert gas atmosphere such as nitrogen or argon.
[0045] (Mixing Step)
[0046] In the mixing step, the solutions prepared in the manner
described above are mixed. There are no particular restrictions on
the order of mixing, and the three solutions may be combined
simultaneously or two of the solutions may be combined and the
remaining one mixed with the obtained mixture.
[0047] The amount of third metal element salt solution used is
preferably 0.01-0.5 mol in terms of the third metal element with
respect to 1 mol of the total of the samarium and cobalt elements
in the samarium and cobalt salts.
[0048] The mixing step is preferably carried out in an inert gas
atmosphere such as nitrogen or argon in order to prevent oxidation
of the Sm, Co and third metal element.
[0049] (Addition Step)
[0050] In this step, a protective agent is added to the mixture
obtained in the mixing step. The protective agent has the function
of protecting the SmCo-based alloy nanoparticles that are produced,
and oleic acid, oleylamine, polyvinylpyrrolidone or polyvinyl
alcohol is preferably used. The protective agent may also be used
in the form of a solution in an organic solvent such as ether.
[0051] The amount of protective agent added is preferably 0.1-20
mol with respect to 1 mol of the total of the samarium and cobalt
elements in the samarium and cobalt salts.
[0052] (Dehydration Step)
[0053] The dehydration step is a step in which the mixture is
stirred and heated under an inert gas flow or under reduced
pressure after inert gas substitution, for dehydration.
Sufficiently reducing the moisture in the mixture can
satisfactorily inhibit oxidation of the reduced Sm or Co. It will
thus be possible to obtain SmCo-based alloy nanoparticles at an
even higher yield.
[0054] Heating of the mixture is preferably carried out at
110-220.degree. C. for 1-24 hours. The mixture is then preferably
cooled to room temperature, and more preferably cooled to
10-30.degree. C. This will allow reduction with the strong reducing
agent in the reduction step described hereunder to be accomplished
in a more reliable manner, so that high-purity SmCo-based alloy
nanoparticles are obtained. If the addition of a strong reducing
agent is under high-temperature conditions (for example, 50.degree.
C. and higher) without cooling, the reduction with the strong
reducing agent will occur all at once, thus tending to result in
production of impurities, such as simple cobalt (Co metal), in
addition to the SmCo-based alloy, and lowering the SmCo-based alloy
content.
[0055] (Reduction Step)
[0056] The reduction step is a step in which, after the strong
reducing agent has been added to the mixture following the
dehydration step, the mixture is stirred and heated to thoroughly
reduce the samarium salt, cobalt salt and third metal element salt
and produce SmCo-based alloy nanoparticles containing the third
metal element.
[0057] The strong reducing agent used may be at least one compound
selected from the group consisting of LiAlH.sub.4, NaBH.sub.1,
N.sub.2H.sub.4, B.sub.2H.sub.6 and LiBH(C.sub.2H.sub.5).sub.3.
These strong reducing agents are preferably added to the mixture
after dissolution in an organic solvent such as an alcohol.
[0058] After addition of the strong reducing agent, an oil bath or
mantle heater is used to keep the mixture at 150-320.degree. C. and
preferably 250-280.degree. C. for 1-3 hours for heated reflux, to
accomplish reduction with the strong reducing agent and the
reducing organic solvent and obtain a reaction mixture. The
reduction reaction reduces the samarium salt, cobalt salt and third
metal element salt. Upon removal of the solvent from the obtained
reaction mixture, SmCo-based alloy nanoparticles containing the
third metal element are obtained.
[0059] Since the third metal element salt is more easily reduced
than the samarium salt and cobalt salt in the reduction reaction
described above, it tends to be reduced earlier than the samarium
salt and cobalt salt. Therefore, the third metal element presumably
acts as nucleus origins for deposition of the SmCo-based alloy. The
presence of the third metal element ensures even smoother reduction
of the samarium salt and cobalt salt, so that the obtained
SmCo-based alloy nanoparticles containing the third metal element
have a sufficiently reduced impurity content.
[0060] The SmCo-based alloy nanoparticles containing the third
metal element can be suitably used as magnetic material because of
both their adequately small particle sizes and excellent magnetic
properties. The particle sizes of the SmCo-based alloy
nanoparticles may be adjusted by varying the amount of protective
agent added and the third metal element content within the ranges
according to the invention, or by varying the temperature and time
for heated reflux in the reduction step.
[0061] The production process of this embodiment allows high-yield
synthesis of SmCo-based alloy nanoparticles containing the third
metal element. The nanoparticles obtained by the production process
of this embodiment may also include nanoparticles composed mainly
of a SmCo-based alloy without the third metal element, or
nanoparticles of the third metal element.
[0062] The embodiment described above is only a preferred
embodiment of the invention, and the invention is in no way limited
thereto.
EXAMPLES
[0063] The present invention will now be explained in greater
detail based on examples and comparative examples, with the
understanding that these examples are in no way limitative on the
invention.
Examples 1-8
Synthesis of SmCo-Based Alloy Nanoparticles
[0064] A first solution was prepared by dissolving 0.33 mmol of
samarium acetylacetonate hydrate
([CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.3Sm.xH.sub.2O) and 0.02-0.5
mmol of the third metal salts listed in Table 1 in 2 ml of
1,2-hexadecanediol (CH.sub.3(CH.sub.2).sub.13CH(OH)CH.sub.2OH)
under a nitrogen atmosphere.
[0065] Separately from this solution, there was prepared a second
solution by dissolving 1.67 mmol of cobalt acetylacetonate
([CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.3Co) in 2 ml of
1,2-hexadecanediol under a nitrogen atmosphere.
[0066] Also, a third solution was prepared by dissolving 3.0 mmol
of oleic acid (CH.sub.3
(CH.sub.2).sub.7CH.dbd.CH(CH.sub.2).sub.7COOH) and 3.0 mmol of
oleylamine
(CH.sub.3(CH.sub.2).sub.7CH.dbd.CH(CH.sub.2).sub.8NH.sub.2) in 40
ml of octyl ether ([CH.sub.3(CH.sub.2).sub.7].sub.2O) under an
inert gas atmosphere (for example, nitrogen or argon).
[0067] The first solution, the second solution and the third
solution were then mixed for about 12 hours using a mechanical
stirrer under a nitrogen atmosphere to obtain a mixture.
[0068] In order to remove the water in the mixture, a three-necked
flask containing the mixture was heated in an oil bath at
200.degree. C. under a nitrogen stream and these conditions were
maintained for about 1 hour, after which it was cooled to room
temperature (about 20.degree. C.). To the cooled mixture there was
added absolute ethanol dissolving 6 mmol of sodium borohydride
(NaBH.sub.4), as a strong reducing agent.
[0069] The temperature of the oil bath was then raised and the
reaction mixture was kept at 250-280.degree. C. for 1-3 hours of
heated reflux. After cooling to room temperature, an ultrafilter
was used for filtration and dehydrated ethanol or the like was used
for solution exchange and washing of the particles. Next, an
evaporator was used to remove the solvent attached to the
particles, and vacuum drying was carried out for 10 hours at
40.degree. C. to obtain particles for Examples 1-8.
[0070] [Evaluation of Particles]
[0071] The particles obtained in Examples 1-8 were observed
(3,000,000 magnification) with a high-resolution TEM (JEM-3010,
trade name of JEOL Corp.). Also, 100 particles were randomly
selected from the electron microscope image, and the mean particle
size was calculated. The mean particle sizes of the synthesized
particles are listed in Table 1.
[0072] The obtained particles were also examined by X-ray
diffraction (XRD) and ICP optical emission spectroscopic analysis.
FIG. 4 shows the XRD results for the synthesized particles, wherein
the upper chart is an XRD chart for the particles obtained in
Example 2. These XRD measurement results confirmed that the
particles synthesized in Example 2 are particles composed mainly of
SmCo.sub.5 (SmCo.sub.5 particles) with an adequately reduced
content of impurities such as oxides. The results of electron
diffraction image analysis using the high-resolution TEM also
confirmed that the synthesized particles were SmCo.sub.5.
[0073] The particles of Example 1 and Examples 3-8 were also
confirmed by XRD and high-resolution TEM analysis to be SmCo.sub.5
particles with adequately reduced contents of impurities such as
oxides. The contents of the third metal elements in the particles
of Examples 1-8 as determined by ICP optical emission spectroscopic
analysis are also listed in Table 1.
[0074] The yields of SmCo.sub.5 particles in Examples 1-8 are also
shown in Table 1. The yields are the total masses of Sm and Co
elements as measured by ICP optical emission spectroscopy, with
respect to the theoretical produced mass of SmCo.sub.5 as
calculated from the amounts of Sm and Co used.
[0075] The evaluation results described above confirmed that the
SmCo.sub.5 nanoparticles containing third metal elements were
obtained at high yield.
[0076] [Evaluation of Magnetic Properties]
[0077] The coercive forces (Hc) of the SmCo.sub.5 nanoparticles of
Examples 1-8 were measured using a VSM (Vibrating Sample
Magnetometer) (VSM-5, trade name of Toei Industry Co., Ltd.), under
conditions with an applied magnetic field of 20 kOe at 25.degree.
C. The results of coercive force measurement are shown in Table 1.
FIG. 5 is a graph showing the magnetic properties of the SmCo.sub.5
nanoparticles of Example 2. The SmCo.sub.5 nanoparticles of Example
1 and Examples 3-8 exhibited satisfactorily excellent magnetic
properties, similar to the SmCo.sub.5 nanoparticles of Example
2.
Example 9
[0078] Particles were obtained by synthesis in the same manner as
Example 2, except that lithium aluminum hydride (LiAlH.sub.4) was
used as the strong reducing agent instead of sodium borohydride.
Evaluation of the particles and their magnetic properties in the
same manner as Example 2 revealed a high yield of SmCo.sub.5
nanoparticles with excellent magnetic properties, containing Cu as
the third metal element. The particle size, third metal element
content, yield and coercive force (Hc) of the SmCo.sub.5
nanoparticles were measured and the results are shown in Table
1.
Comparative Example 1
[0079] SmCo.sub.5 nanoparticles were synthesized in the same manner
as Example 1, except that the third metal salt (palladium
acetylacetonate) and sodium borohydride were not used. The
particles and their magnetic properties were evaluated in the same
manner as Example 1. The lower chart of FIG. 4 is an XRD chart for
the particles obtained in Comparative Example 1. The analysis
results confirmed that the particles contained an abundant amount
of compounds other than the SmCo-based alloy (such as Sm oxides and
Co oxides), and therefore were not composed mainly of the
SmCo-based alloy. The particle size, yield and coercive force (Hc)
of the obtained particles are shown in Table 1.
Comparative Example 2
[0080] Particles were obtained by synthesis in the same manner as
Example 1, except that no sodium borohydride was used. The
particles and their magnetic properties were evaluated in the same
manner as Example 1. The middle chart of FIG. 4 represents XRD
analysis for the particles obtained in Comparative Example 2. The
analysis results confirmed that the particles contained compounds
other than the SmCo-based alloy (such as Sm oxides and Co oxides),
and therefore were not composed mainly of the SmCo-based alloy. The
particle size, third metal element content in the particles, yield
and coercive force (Hc) of the obtained particles are shown in
Table 1.
Comparative Example 3
[0081] Particles were obtained by synthesis in the same manner as
Example 1, except that the third metal element salt (palladium
acetylacetonate) was not used. The particle size, yield and
coercive force (Hc) of the particles are shown in Table 1. The
coercive force (Hc) of the particles of Comparative Example 3 was
lower than that of the SmCo.sub.5 nanoparticles containing third
metal elements of Examples 1-9.
TABLE-US-00001 TABLE 1 Strong Mean particle Third metal element
reducing size Yield Content Hc Third metal element salt agent (nm)
(wt %) Type (wt %) (Oe) Example 1
[CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.2Pd NaBH.sub.4 6 45 Pd 0.76
1010 Example 2 [CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.2Cu NaBH.sub.4
5 66 Cu 0.79 1290 Example 3
[CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.2Cu NaBH.sub.4 12 43 Cu 0.07
1000 Example 4 [CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.2Cu NaBH.sub.4
3 52 Cu 19.46 1030 Example 5
[CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.2Ni.cndot.2H.sub.2O
NaBH.sub.4 5 63 Ni 0.74 1240 Example 6
[CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.2Pt NNaBH.sub.4 4 55 Pt 0.78
1430 Example 7 AuCl NaBH.sub.4 5 58 Au 0.80 1280 Example 8
[CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.3Cr NaBH.sub.4 7 41 Cr 0.69
1040 Example 9 [CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.2Cu
LiAlH.sub.4 6 49 Cu 0.75 1120 Comp. Example 1 None None 30 25 None
0.00 150 Comp. Example 2 [CH.sub.3COCH.dbd.C(O--)CH.sub.3].sub.2Pd
None 9 39 Pd 0.78 700 Comp. Example 3 None NaBH.sub.4 15 30 None
0.00 650
* * * * *