U.S. patent application number 11/080492 was filed with the patent office on 2005-07-21 for nanoparticle, method of producing nanoparticle and magnetic recording medium.
This patent application is currently assigned to FUJI PHOTO FILM CO., LTD.. Invention is credited to Hattori, Yasushi, Waki, Koukichi.
Application Number | 20050158506 11/080492 |
Document ID | / |
Family ID | 27667538 |
Filed Date | 2005-07-21 |
United States Patent
Application |
20050158506 |
Kind Code |
A1 |
Waki, Koukichi ; et
al. |
July 21, 2005 |
Nanoparticle, method of producing nanoparticle and magnetic
recording medium
Abstract
A method of producing a nanoparticle, the method comprising: a
reducing step of adding an reverse micelle solution (II) obtained
by mixing a water-insoluble organic solvent containing a surfactant
with an aqueous metal salt solution to an reverse micelle solution
(I) obtained by mixing a water-insoluble organic solvent containing
a surfactant with an aqueous reducing agent solution, to carry out
a reducing reaction; and a maturing step of raising the temperature
of the reduced mixture to mature the reduced mixture is provided. A
method of producing a plural type alloy nanoparticle, the method
comprising producing a nanoparticle made of a plural type alloy
through a reducing step of mixing one or more reverse micelle
solutions (I) containing a metal salt with an reverse micelle
solution (II) containing a reducing agent to carry out reducing
treatment and a maturing step of carrying out maturing treatment is
also provided.
Inventors: |
Waki, Koukichi; (Kanagawa,
JP) ; Hattori, Yasushi; (Kanagawa, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
FUJI PHOTO FILM CO., LTD.
|
Family ID: |
27667538 |
Appl. No.: |
11/080492 |
Filed: |
March 16, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11080492 |
Mar 16, 2005 |
|
|
|
10367873 |
Feb 19, 2003 |
|
|
|
Current U.S.
Class: |
428/848.1 ;
264/4; G9B/5.238; G9B/5.253 |
Current CPC
Class: |
H01F 10/123 20130101;
G11B 5/65 20130101; B22F 9/24 20130101; B82Y 25/00 20130101; G11B
5/70605 20130101; B22F 1/0018 20130101; H01F 41/30 20130101; B82Y
40/00 20130101; B82Y 30/00 20130101 |
Class at
Publication: |
428/065.3 ;
264/004 |
International
Class: |
A61K 009/14; B29C
039/10; B32B 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2002 |
JP |
2002-039957 |
Jul 19, 2002 |
JP |
2002-211154 |
Claims
1-12. (canceled)
13. A nanoparticle produced by a method comprising a reducing step
of adding an reverse micelle solution (II) obtained by mixing a
water-insoluble organic solvent containing a surfactant with an
aqueous metal salt solution to an reverse micelle solution (I)
obtained by mixing a water-insoluble organic solvent containing a
surfactant with an aqueous reducing agent solution, to carry out a
reducing reaction; and a maturing step of raising the temperature
of the reduced mixture of micelle solutions (I) and (II) to mature
the reduced mixture after the reducing reaction is completed,
wherein the ratio (water/surfactant) by mass of water to the
surfactant in each of the reverse micelle solutions (I) and (II) is
20 or less; the reducing reaction temperature is constant in a
range from -5 to 30.degree. C.; and the maturing temperature is
higher than the reducing reaction temperature and is constant in a
range from 30 to 90.degree. C., and the maturing time is 5 to 180
minutes.
14. A magnetic recording medium comprising at least a magnetic
layer formed on a support, wherein the magnetic layer is formed by
applying a dispersion solution in which a nanoparticle is dispersed
to the support and an annealing treatment is performed; the
nanoparticle being produced by a method comprising a reducing step
of adding an reverse micelle solution (II) obtained by mixing a
water-insoluble organic solvent containing a surfactant with an
aqueous metal salt solution to an reverse micelle solution (I)
obtained by mixing a water-insoluble organic solvent containing a
surfactant with an aqueous reducing agent solution, to carry out a
reducing reaction; and a maturing step of raising the temperature
of the reduced mixture of micelle solutions (I) and (II) to mature
the reduced mixture, and the ratio (water/surfactant) by mass of
water to the surfactant in each of the reverse micelle solutions
(I) and (II) is 20 or less; the reducing reaction temperature is
constant in a range from -5 to 30.degree. C.; and the maturing
temperature is higher than the reducing reaction temperature and is
constant in a range from 30 to 90.degree. C., and the maturing time
is 5 to 180 minutes.
15-18. (canceled)
19. A nanoparticle that is made of a plural type alloy through a
reducing step of mixing one or more reverse micelle solutions (I)
containing a metal salt with an reverse micelle solution (II)
containing a reducing agent to carry out reducing treatment and a
maturing step of carrying out maturing treatment after the reducing
treatment, wherein at least two metals constituting the plural type
alloy are selected from the VIb group and VIII group in the
periodic table; and at least one metal constituting the plural type
alloy is selected from the Ib group, IIIa group, IVa group and Va
group and the content of the selected metals is 1 to 30 at. % in
all of the plural type alloy.
20. The nanoparticle of claim 19, wherein the coefficient of
variation in the particle diameter distribution of the
nanoparticles.
21. A magnetic recording medium comprising at least a magnetic
layer formed on a support, wherein; the magnetic layer is formed by
applying a dispersion solution prepared by dispersing nanoparticles
and by carrying out annealing treatment, wherein the nanoparticles
are made of a plural type alloy through a reducing step of mixing
one or more reverse micelle solutions (I) containing a metal salt
with an reverse micelle solution (II) containing a reducing agent
to carry out reducing treatment and a maturing step of carrying out
maturing treatment after the reducing treatment, wherein at least
two metals constituting the plural type alloy are selected from the
VIb group and VIII group in the periodic table; and at least one
metal constituting the plural type alloy is selected from the Ib
group, IIIa group, IVa group and Va group and the content of the
selected metals is 1 to 30 at. % in all of the plural type
alloy.
22. The magnetic recording medium of claim 21, wherein the coercive
force of the nanoparticle is 95.5 to 1193.8 KA/m (1200 to 15000
Oe).
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a nanoparticle, a method of
producing a nanoparticle, and a magnetic recording medium
[0003] 2. Description of the Related Art
[0004] In order to increase magnetic recording density, it is
necessary to decrease the particle size of magnetic bodies
contained in a magnetic layer. In magnetic recording media used
widely in videotapes, computer tapes, disks, and the like, noise
decreases with the decrease in particle size when the mass of the
ferromagnetic body is the same.
[0005] CuAu type or Cu.sub.3Au type hard magnetic regular alloys
have large crystal magnetic anisotropy because of distortion caused
when regulated so that they exhibit hard magnetic characteristics
even if they are reduced in particle size and put in a nanoparticle
state. Therefore, these alloys are promising materials for
improving magnetic g density.
[0006] Examples of methods for synthesizing nanoparticles capable
of forming these CuAu type or Cu.sub.3Au type alloys when
classified by precipitation method include (1) an alcohol reduction
method using a primary alcohol; (2) a polyol reduction method using
a secondary, tertiary, divalent or trivalent alcohol; (3) a heat
decomposition method; (4) an ultrasonic decomposition method; and
(5) a strong reducing agent reduction method.
[0007] Also, when classified by a reaction system, methods for
synthesizing nanoparticles include (6) a polymer existence method;
(7) a high-boiling point solvent method; (8) a regular micelle
method; and (9) an reverse micelle method.
[0008] The alcohol reduction method (1) has poor reduction ability.
Therefore, when reducing a precious metal and a base metal at the
same time, it is hard to form a uniform alloy and many alloys end
up having a core/shell structure. In the case of the polyol
reduction method (2) and the heat decomposition method (3), a
high-temperature reaction is required and these methods are
therefore inferior in production aptitude. The ultrasonic
decomposition method (4) and the strong reducing agent reduction
method (5) are relatively simple methods. However, in these
methods, coagulation and precipitation tend to be caused and it is
therefore difficult to obtain a small monodispersible particle
without implementing a special technique in the reaction
system.
[0009] There is also an ethanol reduction method using
polyvinylpyrrolidone, in which the above-mentioned methods (1) and
(6) are combined. In this case, the amount of polymers after
synthesis is very large and is difficult to decrease to the
required amount.
[0010] For a system in which methods (2), (3) and (7) are combined,
those described in Japanese Patent Application Laid-Open (JP-A) No.
2000-54012 and U.S. Pat. No. 6,254,662 are known. This method is,
however, very hazardous because highly toxic substances are used.
Also, in these methods, it is necessary to run a reaction in inert
gas and at a temperature as high as nearly 300.degree. C., hence
these methods have the drawback that the apparatuses used are
complicated and thus inferior from the standpoint of production
aptitude.
[0011] Methods using a system combining methods (5) and (8) and a
system combining methods (5) and (9) are common methods. However,
detailed conditions and the like as to a method for obtaining metal
nanoparticles having the intended composition and particle size
have yet to be found.
[0012] The nanoparticles synthesized in the above methods have a
face-centered cubic crystal structure. The face-centered cubic
crystal usually exhibits soft magnetism or paramagnetism. These
nanoparticles exhibiting soft magnetism or paramagnetism are not
adaptable to recording media. In order to obtain a hard magnetic
regular alloy having a coercive force of 95.5 kA/m (1200 Oe) or
more, which is necessary for magnetic recording media, annealing
treatment must be carried out at a temperate higher than the
transformation temperature at which the alloy is transformed from
an irregular phase to a regular phase.
[0013] However, when the nanoparticle produced in the above methods
is applied to a support, followed by annealing treatment to produce
a magnetic recording medium, these nanoparticles tend to coagulate
easily with each other leading to reduced coatability and
deteriorated magnetic characteristics. It is also difficult to form
a perfect regular phase even if heat treatment is performed because
the particle diameter of the resulting nanoparticle is uneven and
therefore, there are cases where the desired hard magnetism is not
obtained.
[0014] Also, the transformation temperature is generally as high as
500.degree. C. or more and an organic support, which is commonly
used, does not possess adequate heat resistance. It is therefore
difficult to form a magnetic film by applying a nanoparticle to the
organic support, followed by carrying out annealing treatment.
SUMMARY OF THE INVENTION
[0015] In this situation, it is an object of the present invention
to provide nanoparticles which are not easily coagulated with each
other, have high coatability and of which the particle size and
composition can be controlled and also to provide a method of
producing the nanoparticle. Also, another object of the invention
to provide a magnetic recording medium which contains the above
nanoparticle in a magnetic layer and exhibits hard magnetism.
[0016] The inventors of the invention have made earnest studies to
solve the above problem and, as a result, found that the above
problem can be solved by the following invention. Accordingly, the
first embodiment of the invention provides a method of producing a
nanoparticle, the method comprising a reducing step of adding an
reverse micelle solution (II) obtained by mixing a water-insoluble
organic solvent containing a surfactant with an aqueous metal salt
solution to an reverse micelle solution (I) obtained by mixing a
water-insoluble organic solvent containing a surfactant with an
aqueous reducing agent solution, to carry out a reducing reaction
and a maturing step of raising the temperature of the system to
mature the system after the reducing reaction is finished, wherein
the ratio (water/surfactant) by mass of water to the surfactant in
each of the reverse micelle solution (I) and the reverse micelle
solution (II) is 20 or less; the reducing reaction temperature is
constant in a range from -5 to 30.degree. C.; and the maturing
temperature is higher than the reducing reaction temperature and is
constant in a range from 30 to 90.degree. C. and the maturing time
is 5 to 180 minutes.
[0017] Further, from the above point view, it is an object of the
present invention to provide a method of producing a plural type
alloy nanoparticle which has a low transformation temperature, is
scarcely coagulated, has superior coatability, has also a
controllable particle se and composition and can exhibit
ferromagnetism in a high yield.
[0018] Thus, the second embodiment of the invention resides in a
method of producing a plural type nanoparticle, the method
comprising producing a nanoparticle made of a plural type alloy
through a reducing step of mixing one or more reverse micelle
solutions (I) containing a metal salt with an reverse micelle
solution (II) containing a reducing agent to carry out reducing
treatment and a maturing step of out maturing treatment after the
reducing treatment, wherein
[0019] at least two metals constituting the plural type alloy are
selected from the VIb group and VIII group in the periodic table;
and
[0020] at least one metal constituting the plural type alloy is
selected from the lb group, IIIa group, IVa group and Va group and
the content of the selected metal is to 30 at. % in all of the
plural type alloy.
[0021] In the case where at least two metals constituting the
plural type alloy are selected from the VIb group or VIII group in
the periodic table in order to develop ferromagnetism and hard
magnetism, it is preferable that a CuAu type or Cu.sub.3Au type
alloy be formed of these metals.
[0022] The methods of embodiments 1 and 2 preferably further
comprise a washing/dispersing step of washing the matured solution
by a mixed solution of water and a primary alcohol after the
maturing step is finished, then carrying out precipitating
treatment by using a primary alcohol to produce a precipitate and
dispersing the precipitate by using an organic solvent.
[0023] Further, at least one dispersant having 1 to 3 amino groups
or carboxyl groups is preferably added to at least any one of the
reverse micelle solutions (I) and (II) in an amount of 0.001 to 10
mol per one mol of the metal nanoparticle intended to be
produced.
[0024] Also, the invention provides a nanoparticle produced by the
aforementioned method of producing a nanoparticle.
[0025] Further, the invention provides a magnetic recording medium
comprising a magnetic layer formed on a support, wherein;
[0026] the magnetic layer is formed by applying a dispersion
solution in which the aforementioned nanoparticle is dispersed to
the support and performing annealing treatment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] Method of Producing Nanoparticles
[0028] A method of producing a nanoparticle according to the
present invention comprises a reducing step of mixing at least two
reverse micelle solutions to run a reducing reaction and a maturing
step of maturing the resulting solution at a predetermined
temperature after the reducing reaction is finished. Specifically,
the method of producing a nanoparticle according to the embodiment
2 of the present invention comprises a reducing step of mixing one
or more reverse micelle solutions (I) containing a metal salt with
an inverse solution (II) containing a reducing agent to carry out
reducing treatment and a maturing step of carrying out maturing
treatment after the reducing treatment. A plural type alloy
nanoparticle (hereinafter refereed to simply as "nanoparticle" as
the case may be) is produced by the above production method.
[0029] Each step will be explained hereinbelow.
[0030] Reducing Step
[0031] First, a water-insoluble organic solvent containing a
surfactant is mixed with an aqueous reducing agent solution to
prepare an reverse micelle solution (I).
[0032] As the surfactant, an oil-soluble surfactant is used.
Specific examples of the oil-soluble surfactant include sulfonate
types (e.g., Aerosol OT (manufactured by Wako Pure Chemical
Industries, Ltd.), quaternary ammonium salt types (e.g.,
cetyltrimethylammonium bromide) and ether types (e.g.,
pentaethylene glycol dodecyl ether).
[0033] The water-insoluble organic solvent used to dissolve the
foregoing surfactant is alkanes and ethers. The Ones are preferably
those having 7 to 12 carbon atoms. Specifically, heptane, octane,
nonane, decane, undecane and dodecane are preferable. The ethers
are preferably diethyl ether, dipropyl ether and dibutyl ether.
[0034] The amount of the surfactant in the water-insoluble organic
solvent is preferably 20 to 200 g/l.
[0035] As the reducing agent in the aqueous reducing agent
solution, alcohols; polyalcohols; H.sub.2; compounds containing
HCHO, S.sub.2O.sub.6.sup.2-, H.sub.2PO.sub.2.sup.-, BH.sub.4.sup.-,
N.sub.2H.sub.5.sup.+, H.sub.2PO.sub.3.sup.- and the like may be
used either singly or in combinations of two or more.
[0036] The amount of the reducing agent in the aqueous solution is
preferably 3 to 50 mol based on one mol of the metal salt.
[0037] Here, the ratio (water/surfactant) by mass of water to the
suractant in the reverse micelle solution (I) is designed to be 20
or less. When the mass ratio exceeds 20, such a problem arises that
precipitation tends to be caused and the particles tend to be
uneven. The ratio by mass is preferably 15 or less and more
preferably 0.5 to 10.
[0038] Besides the above micelle solution (I), an reverse micelle
solution (II) is prepare which is obtained by mixing a
water-insoluble organic solvent containing a surfactant with an
aqueous metal salt solution of the first embodiment of the
invention.
[0039] The conditions (e.g., materials to be used and
concentration) of the surfactant and water-insoluble organic
solvent are the same as those used for the micelle solution (I). It
is to be noted that either the same type or different types as that
of the reverse micelle solution (I) may be used Also, the ratio by
mass of water to the surfactant in the reverse micelle solution
(II) is the same as that in the reverse micelle solution (I) and
may be the same as or different from that in the reverse micelle
solution (I).
[0040] In the second embodiment of the invention, a water-insoluble
organic solvent containing a surfactant is firstly mixed with an
aqueous metal salt solution to prepare an inverse solution (I). The
reverse micelle solution (I) may contain plural metal alts which
are used to produce a plural type alloy. Also, these metal salts
may be made to be contained in separate solutions, which may be
respectively prepared as reverse micelle solutions (I).
[0041] For example, an reverse micelle solution (I.sub.a)
containing metals selected from the VIb group and VIII group and an
reverse micelle solution (I.sub.b) containing metals selected from
the Ib group, IIIa group, IVa group and Va group may be separately
prepared and mixed optionally.
[0042] As the metal salt to be contained in the aqueous meal salt
solution of the first embodiment and the second embodiment of the
invention, a metal salt selected arbitrarily from nitrates,
sulfates, chlorides, acetates, acetylacetonates, hydroacids of
metal complexes using a chlorine ion as a ligand, potassium salts
of metal complexes using a chlorine ion as a ligand, sodium salts
of metal complexes using a chlorine ion as a ligand, ammonium salts
of metal complexes using an oxalic acid ion as a ligand may be
used.
[0043] Also, as the metals, at least two types are selected from
the VIb group and VIII group and at least one type is selected from
the Ib group, IIIa group, IVa group and Va group.
[0044] A nanoparticle capable of exhibiting hard magnetism is
produced by using metals selected from the VIb group and VIII
group. Also, the use of metals selected from the Ib group, IIIa
group, IVa group and Va group makes it possible to lower the phase
transformation temperature at which the hard magnetism of the
nanoparticle is developed. As a consequence, the necessity for
considering the heat resistance of a support and the like is thus
obviated when it is intended to produce a magnetic recording medium
or the like by using the nanoparticle and it is therefore possible
to form a magnetic layer containing the nanoparticle on a support
made of an organic material in an efficient manner.
[0045] In the first embodiment and the second embodiment of the
invention, examples of a binary and a ternary alloy composition
constituted of the VIb group and VIII group, namely, CuAu type or
Cu.sub.3Au type ferromagnetic regular alloy include FePt, FePd,
FeNi, CoPt, CoPd, CoAu, CoCrPt, CoCrPd, FeNiPt, FeCoPt, Ni.sub.3Fe,
FePd.sub.3, Fe.sub.3Pt, FePt.sub.3, CoPt.sub.3, Ni.sub.3Pt, and
CrPt.sub.3.
[0046] The other element selected from the Ib group, IIIa group,
IVa group and Va group and contained to produce the plural type
alloy is preferably selected from Cu, Ag, B, In, Sn, Pb, P, Sb and
Bi. The amount (content) of the element selected from the Ib group,
IIIa group, IVa group and Va group is designed to be 1 to 30 at. %
and preferably 5 to 20 at. % based on all the plural type
alloy.
[0047] If the amount is less than 1 at. %, the effect of dropping
the transformation temperature is decreased and the addition has no
significance. If the amount exceeds 30 at. %, aregularphase in
which the crystal structure of the nanoparticle has hard magnetism
after annealing treatment cannot be formed eventually.
[0048] It is to be noted that the plural type alloy is preferably
constituted of a total of 3 to 5 elements including the two
elements selected from the VIb group and VIII group and one element
selected from the Ib group, IIIa group, IVa group and Va group.
[0049] The concentration (as metal salt concentration) of each
element in the aqueous metal salt solution is preferably 0.1 to
2000 .mu.mol/ml and more preferably 1 to 500 .mu.mol/ml.
[0050] It is preferable to add a chelating agent to the aqueous
metal salt solution to make each resulting particle have an even
composition. The chelate stability constant (log K) is preferably
10 or less. Specifically, it is preferable to use, for example,
DHEG (dihydroxyethylglycine), IDA (iminodiacetic acid), NTP
(nitrilotripropionic acid), HIDA (dihydroxyethyliminodiacetic
acid), EDDP (ethylenediaminedipropionic acid dihydrochloride),
BAPTA (tetrapotassium diaminophenylethylene glycol tetraacetate
hydride) or the like.
[0051] The amount of the chelating agent is preferably 0.1 to 10
mol and more preferably 0.3 to 3 mol per one mol of the metal
salt.
[0052] Next, in the second embodiment of the invention, a
water-insoluble organic solvent containing a surfactant is mixed
with an aqueous reducing agent solution to prepare an reverse
micelle solution (II). When two or more reducing agents are used,
these reducing agents may be mixed together to prepare an inverse
solution (II). However, it is desirable that these reducing agents
be preferably mixed separately with a water-insoluble organic
solvent to prepare separate reverse micelle solutions (II.sub.a),
(II.sub.b), (II.sub.c) etc., and these solutions be used by mixing
arbitrarily taking, for example, solution stability and operability
into account.
[0053] The conditions (e.g., materials to be used and
concentration) of the surfactant, water-insoluble organic solvent,
and reducing agent are the same as those used for the micelle
solution (I) of the first embodiment of the invention.
[0054] The ratios by mass of water to the surfactant in the reverse
micelle solutions (I) and (II) may be the same or different;
however, the ratios are preferably the same to make the system
uniform.
[0055] In both of the first and the second embodiments of the
invention, the prepared reverse micelle solutions (I) and (II) are
mixed with each other in the above manner. Although there is no
particular limitation to a mixing method, it is preferable to mix
the both by adding the reverse micelle solution (II) to the reverse
micelle solution (I) with stirring the reverse micelle solution (I)
taking reduction uniformity into account. After the mixing is
finished, a reducing reaction is made to run. At this time, the
temperature is made to be constant in a range from -5 to 30.degree.
C.
[0056] When the reducing temperature is less than -5.degree. C.,
such a problem that the water phase is congealed, causing an uneven
reducing reaction. When the reducing temperature exceeds 30.degree.
C., coagulation or precipitation tends to be caused, making the
system unstable. The reducing temperature is preferably 0 to
25.degree. C. and more preferably 5 to 25.degree. C.
[0057] Here, the foregoing term "constant temperature" means that
when the set temperature is T (.degree. C.), the temperature T
falls in a range of T.+-.3.degree. C. It is to be noted that even
in the case of setting the constant temperature in this manner, the
upper limit and lower limit of T fall in the above reducing
temperature range (-5 to 30.degree. C.).
[0058] Although it is necessary to set the reducing reaction time
appropriately according to the amount of the reverse micelle
solution and the like, the reaction time is preferably 1 to 30
minutes and more preferably 5 to 20 minutes.
[0059] Because the reducing reaction greatly affects the
monodispersibility of the distribution of particle diameter, it is
preferable to run the reducing reaction with stirring at a rate as
high as possible (for example, at about 3,000 rpm or faster).
[0060] A preferable stirring apparatus is a stirrer having high
shearing force and is specifically a stirrer having a structure in
which the stirring blade basically has a turbine type or paddle
type structure, also a sharp edge is attached to a position where
it is in contact with the end of the blade or with the blade and
the blade is rotated using a motor. Specifically, as the stirrer, a
dissolver (manufactured by Tokushu Kika Kogyo Co., Ltd.), Omni
Mixer (manufactured by Yamato Scientific Co., Ltd.) and homogenizer
(manufactured by SMT) are useful. The use of each of these
apparatuses makes it possible to synthesize a monodispersible
nanoparticle in the form of a dispersion solution.
[0061] It is preferable to add at least one dispersant having 1 to
3 amino groups or carboxyl groups to at least any one of the above
micelle solutions (I) and (II) in an amount of 0.001 to 10 mol per
1 mol of the metal nanoparticle to be produced.
[0062] The addition of such a dispersant ensures that a
nanoparticle which is more improved in monodispersibility and is
free from coagulation can be obtained.
[0063] When the amount of the dispersant is less than 0.001, there
is the case where the monodispersibility of the nanoparticle cannot
be more improved, whereas when the amount exceeds 10 mol, there is
the case where coagulation arises.
[0064] As the aforementioned dispersant, organic compounds having a
group which adsorbs to the surface of the metal nanoparticle are
preferable. Specific examples of the dispersant include organic
compounds having 1 to 3 amino groups, carboxy groups, sulfonic acid
groups or sulfinic acid groups. These organic compounds may be used
either singly or in combinations of two or more.
[0065] These examples are compounds having the structural formulae
represented by R--NH.sub.2, NH.sub.2--R--NH.sub.2,
NH.sub.2--R(NH.sub.2)--NH.sub.2, R--COOH, COOH--R--COOH,
COOH--R(COOH)--COOH, R--SO.sub.3H, SO.sub.3H--R--SO.sub.3H,
SO.sub.3H--R(SO.sub.3H)--SO.sub.3H, R--SO.sub.2H,
SO.sub.2H--R--SO.sub.2H and SO.sub.2H--R(SO.sub.2H)--SO.sub.2H,
wherein R represents a straight-chain, branched or cyclic saturated
or unsaturated hydrocarbon.
[0066] A compound particularly preferable as the dispersant is
oleic acid. Oleic acid is a surfactant known in point of
stabilizing a colloid and has been used to protect an iron
nanoparticle. Oleic acid is provided with a relatively long chain
(for example, oleic acid has 18 carbon chains and a length of 20
angstroms (2 nm) or more and is not an aliphatic compound but has
one double bond) which provides an important steric hindrance which
offsets a strong interaction between particles.
[0067] Like oleic acid, long-chain carboxylic acids such as erucic
acid and linoleic acid are used (for example, long-chain organic
acids having 8 to 22 carbon atoms may be used either singly or in
combinations of two or more). Oleic acid (e.g., olive oil) is an
easily available and inexpensive natural resource and is therefore
preferable. Also, like oleic acid, oleylamine derived from oleic
acid is a useful dispersant.
[0068] It is considered that in the above reducing step, metals,
such as Co, Fe, Ni and Cr, of which the redox potential is on a
lower level (metals whose redox potential is the order of -0.2 V or
less (vs. N. H. E)) in the CuAu type or Cu.sub.3Au type hard
magnetic regular alloy phase are reduced and precipitated in a
micro-sized and monodispersed state. Thereafter, in a stage of
raising temperate or in a maturing step which will be described
later, the precipitated base metal serves as a nucleus, on the
surface of which metals, such as Pt, Pd and Rh, of which the redox
potential is on a higher level (metals whose redox potential is the
order of -0.2 V or more (vs. N. H. B)) are reduced by the base
metal substituted and precipitated. It is considered that the
ionized base metal is rereduced by a reducing agent and
precipitated. Such a process is repeated to obtain a nanoparticle
capable of forming a CuAu type or Cu.sub.3Au type hard magnetic
regular alloy.
[0069] Maturing Step
[0070] After the reducing reaction is finished, the solution after
the reaction is raised to maturing temperature.
[0071] Although the mating temperature is preferably set to a
constant temperature in a range from 30 to 90.degree. C., its
temperature is made to be higher than the temperature used in the
reducing reaction. Also, the mating time is preferably set to 5 to
180 minutes. When the maturing temperature and time are shifted to
the high-temperature and long-time side, coagulation and
precipitation tend to be caused. When, on the contrary, the
maturing temperature and time are shifted to the low-temperature
and short-time side, the reaction is not completed, causing a
change in composition. The maturing temperature and time are
preferably 40 to 80.degree. C. and 10 to 150 minutes and more
preferably 40 to 70.degree. C. and 20 to 120 minutes
respectively.
[0072] Here, the aforementioned term "constant temperature" has the
same meanings as in the case of the temperature in the reducing
reaction (provided that the "reducing temperature" is changed to
the "maturing temperature"). Particularly, the maturing temperature
is higher than the aforementioned temperature used in the reducing
reaction by preferably 5.degree. C. or more and more preferably
10.degree. C. or more within the aforementioned maturing
temperature range (30 to 90.degree. C.). When a difference in
temperature between the both is less than 5.degree. C., there is
the case where a composition according to the formulation is not
obtained.
[0073] In the maturing step as aforementioned, a precious metal is
precipitated on the base metal which has been reduced and
precipitated in the reducing step. Namely, the precious metal is
reduced only on the base metal and therefore the base metal and the
precious metal are not precipitated separately. It is therefore
possible to produce a nanoparticle, capable of efficiently forming
a CuAu type or Cu.sub.3Au type hard magnetic regular alloy, in a
high yield according to the formulated percentage composition,
whereby the nanoparticle can be controlled so as to have a desired
composition. Also, the resulting nanoparticle can be made to have a
desired particle diameter by appropriately regulating stirring
speed at the temperature in the maturing.
[0074] It is preferable to provide a washing/dispersing step in
which after the above maturing is carried out, the mated solution
is washed using a mixed solution of water and a primary alcohol and
then, precipitation treatment is carried out using a primary
alcohol to produce a precipitate, which is then dispersed using an
organic solvent.
[0075] The provision of such a washing step ensures that impurities
are removed to thereby improve the coatability exhibited when
forming the magnetic layer of the magnetic recording medium by
application.
[0076] The aforementioned washing and dispersion are respectively
carried out at least once and preferably twice or more.
[0077] Although there is no particular limitation to the
aforementioned primary alcohol used in the washing step, methanol,
ethanol or the like is preferable. The ratio by volume of
(water/primary alcohol) is preferably in a range from 10/1 to 2/1
and more preferably in a range from 5/1 to 3/1.
[0078] If the ratio of water is high, there is the case where the
surfactant is removed with difficulty, whereas if the ratio of the
primary alcohol is high, there is the case where coagulation takes
place.
[0079] A nanoparticle dispersed in a solution is obtained in the
above manner. These nanoparticles are monodispersible. Therefore,
even if these particles are applied to a support, these particle
are not coagulated but kept in a uniformly dispersed state. These
nanoparticles are not coagulated with each other even if annealing
treatment is carried out and can be therefore hard-magnetized
efficiently, showing that these nanoparticles have high
coatability.
[0080] The particle diameter of the nanoparticle before annealed is
preferably 1 to 20 nm and more preferably 3 to 10 nm. When the
nanoparticles are used for a magnetic recording medium, it is
preferable, that the nanoparticles be closely packed with the view
of increasing recording capacity. For this, the coefficient of
variation of the metal nanoparticles of the invention is preferably
less than 15% and more preferably 8% or less. If the particle size
of the nanoparticle is excessively small the nanoparticle has
superparamagnetism because of thermal fluctuation and such a size
is undesirable. Although the minimum stable particle diameter
differs depending on the structural elements, it is effective to
change the ratio by mass of H.sub.2O/surfactant in the synthesis of
the nanoparticle to obtain a necessary particle diameter.
[0081] In the evaluation of the particle diameter of the
nanoparticle of the invention, a transmission type electron
microscope (TEM) may be used. Although electron beam diffraction
using TEM may be utilized to determine the crystal type of
nanoparticle which is hard-magnetized by heating, it is preferable
to use X-ray analysis to make evaluation with high accuracy. It is
preferable that an FE-TEM capable of finely contracting electron
beams be equipped with an EDAX to make evaluation for the analysis
of the composition inside of the hard-magnetized nanoparticle. A
VSM may be used to evaluate the magnetic qualities of the
hard-magnetized nanoparticle.
[0082] The coercive force of the nanoparticle after annealed is
preferably 95.5 to 1193.8 kA/m (1200 to 15000 Oe) and more
preferably 95.5 to 398 kA/m (1200 to 5000 Oe) from the viewpoint
that when the nanoparticle is applied to the magnetic recording
medium, a recoding head can respond to this.
[0083] Although a method of heating the nanoparticles to a
temperature higher than the transformation temperature is optional
it is preferable to heat after the nanoparticles are applied to a
support to avoid the fusion of these nanoparticles.
[0084] In the case of heating after the nanoparticles are applied
to an organic support having a low heat resistance, it is
preferable to use a pulse laser.
[0085] Because the nanoparticle obtained by the production method
of the second embodiment of the present invention specifically has
a low trans formation temperature, it can also be used for an
organic support having low heat-resistance. In this case, if a
pulse laser is used as means for heating to the transformation
temperature, the deterioration and deformation of the organic
support caused by heat can be prevented more efficiently.
[0086] The hard-magnetized nanoparticle is preferably used in
videotapes, computer tapes, floppy (R) disks and hard disks. It is
also preferably applied to MRAMs.
[0087] Magnetic Recoding Medium
[0088] The magnetic recording medium of the invention comprises at
least a magnetic layer formed on a support and the magnetic layer
contains the nanoparticle obtained by the production method of the
invention. The magnetic layer is formed by applying a coating
solution, in which the nanoparticle is dispersed, to the support,
followed by annealing treatment. Also, the magnetic recording
medium comprises other layers if necessary.
[0089] Namely, the magnetic recording medium of the invention
comprises the magnetic layer containing the nanoparticle on the
surface of the support and also provided with a nonmagnetic layer
between the magnetic layer and the support if necessary. In the
case of a disk, a magnetic layer is likewise formed or a magnetic
layer and a nonmagnetic layer if necessary on the opposite side of
the support. In the case of a tape, for example, a back coat layer
is formed on the side opposite to the magnetic layer on the
support.
[0090] A method of producing a magnetic recording medium in which
the nanoparticle obtained by the production method of the invention
is preferably used will be hereinafter explained in detail and the
magnetic recording medium of the invention will be explained in
detail through the production method.
[0091] As the coating solution in which the nanoparticle is
dispersed, the solution containing the nanoparticle obtained in the
aforementioned method of producing the nanoparticle may be used In
actual, it is preferable to add known additives and various
solvents to the coating solution containing the nanoparticle to
thereby adjust the content of the nanoparicle to a desired one
(0.01 to 0.1 mg/ml).
[0092] The coating solution is applied to the support to form a
lower coating layer or a magnetic layer. In the production of the
magnetic recording medium of the invention, for example, the
foregoing coating solution is applied to the surface of the support
such that the layer thickness of the magnetic layer after dried is
within a range preferably from 5 nm to 200 nm and more preferably
from 5 nm to 100 nm.
[0093] Here, plural coating solutions may be applied one after
another or simultaneously to form a multilayer.
[0094] As a method of applying the coating solution, air doctor
coating, blade coating, rod coating, extrusion coating, air knife
coating, squeeze coating, impregnation coating, reverse roll
coating, transfer roll coating, gravure coating, kiss coating, cast
coating, spray coating and spin coating may be utilized.
[0095] As the support, any of inorganic materials and organic
materials may be used. As the support of an inorganic material, Al,
an Al--Mg alloy, a Mg alloy such as a Mg--Al--Zn alloy, glass,
quartz, carbon, silicon and ceramics may be used. Supports made of
these materials have high impact resistance and also rigidity
coping with an improvement in a thinner support and with high
rotation. Also, these supports have the characteristics that they
are stronger Man organic supports against heat.
[0096] Polyesters such as polyethylene terephthalate and
polyethylene naphthalate, polyolefins, cellulose triacetate,
polycarbonates, polyamides (including aliphatic polyamides and
aromatic polyamides such as alamide), polyimides, polyamidoimides,
polysulfones and polybenzoxazole may be used for the support of an
organic material.
[0097] The nanoparticles prior to annealing treatment has an
irregular phase. In order to obtain a regular phase, it is
necessary to carry out annealing treatment. In the annealing
treatment, the substrate is preferably heated after the coating
operation to avoid the fusion of the particles. As to heating
temperature, the regular-irregular transformation temperature of
the alloy constituting the nanoparticles is found using
differential thermal analysis (DTA) to carry out the annealing
treatment at temperatures higher than the transformation
temperature.
[0098] It is to be noted that the transformation temperature is
changed according to the elemental composition or by the
introduction of third elements.
[0099] In the case of using a support made of an organic material,
it is effective to use a nanoparticle having a transformation
temperature lower than the heat-resistant temperature of the
support or to heat only the magnetic layer by using a pulse
laser.
[0100] Although as the wavelength of a laser in the case of using a
pulse, laser, a wavelength ranging from the ultraviolet region to
the infrared region may be used, laser light having a wavelength
ranging from the visible region to the i,red region is preferably
used because the organic support has absorption in the ultraviolet
region.
[0101] The power of the laser is preferably 0.1 W or more and more
preferably 0.3 W or more because the coating layer is heated in a
short time. When the power is excessively high, there is the case
where the organic support is affected by heat. Therefore, the power
is preferably 3 W or less.
[0102] Examples of a laser which is preferably used include an Ar
ion laser, Cu vapor laser, HF chemical laser, dye laser, ruby
laser, YAG laser, glass Laser, titanium sapphire laser, alexandrite
laser and GaAlAs array semiconductor laser from the viewpoint of
the wavelength of the laser and output.
[0103] The linear velocity when scanning laser light is preferably
1 to 10 m/s and mom preferably 2 to 5 m/s to obtain such an effect
that the laser light causes sufficient annealing but causes no
abrasion.
[0104] It is effective to improve wear resistance by forming a very
thin protective layer on the magnetic layer and further a lubricant
is applied thereon to thereby improve lubricity, thereby securing
full reliability.
[0105] Examples of the protective layer include those comprising
oxides such as silica, alumina, titania, zirconia, cobalt oxide and
nickel oxide; nitrides such as titanium nitride, silicon nitride
and boron nitride; carbides such as silicon carbide, chromium
carbide and boron carbide; and carbons such as graphite and
amorphous carbon. Among these materials, a carbon protective layer
made of carbon is preferable. A carbon protective layer made of
hard amorphous carbon generically called diamond-like carbon is
particularly preferable.
[0106] As a method of producing a carbon protective layer, a
sputtering method is generally used in the case of a hd disk. Many
methods using plasma CVD having a high filming rate are proposed in
the case of products, such as videotapes, which need continuous
filming. It is reported that among these methods, a plasma
injection CVD (PI--CVD) method has a very high filming rate and as
a carbon protective layer to be obtained, a hard and high quality
protective layer reduced in pinholes is obtained (e.g., JP-A Nos.
61-130487, 63-279426 and 3-113824).
[0107] The carbon protective layer is a hard carbon layer having a
Vickers hardness of 1000 Kg/mm.sup.2 or more and preferably 2000
Kg/mm.sup.2 or more. Also, the crystal structure of the carbon
protective layer is an amorphous structure and is nonconductive. In
the case of using a diamond-like carbon layer is used as the carbon
protective Layer, the structure of the carbon layer can be
confirmed by detecting a peak at 1520 to 1560 cm.sup.-1 when
measuring the structure by Raman light spectal analysis. When the
layer structure is deviated from a diamond-like structure, the peak
detected by Raman light spectral analysis is deviated from the
above range and also the hardness of the layer is decreased.
[0108] As raw materials used to produce the carbon protective
layer, carbon-containing compounds including alkanes such as
methane, ethane, propane and butane; alkenes such as ethylene and
propylene; and alkines such as acetylene may be used. Also, a
carrier gas such as argon and addition gases such as hydrogen and
nitrogen for improving layer quality may be added if necessary.
[0109] When the layer thickness of the carbon protective layer is
high, this brings about deteriorated electromagnetic transformation
characteristics and a reaction in adhesiveness to the magnetic
layer, whereas when the layer thickness is low, this brings about a
lack of wear resistance. Therefore, the layer thickness is
preferably 2.5 to 20 nm and more preferably 5 to 10 nm. Also, in
order to improve adhesion between this hard carbon protective layer
and the ferromagnetic metal thin layer which is to be the support,
the surface of the ferromagnetic metal thin layer may be etched in
advance by inert gas or exposed to a plasma of reactive gas such as
oxygen to reform the surface.
[0110] The magnetic layer may be made to have a multilayer
structure to improve electromagnetic transformation characteristics
or may be provided with a nonmagnetic base layer or an intermediate
layer.
[0111] In the magnetic recording medium of the invention, it is
preferable to provide a lubricant and a rust preventive agent to
the surface of the magnetic layer or to the surface of the
protective layer to improve running durability and corrosion
resistance. As the lubricant to be added, known hydrocarbon type
lubricants, fluorine type lubricants and extreme-pressure type
additives may be used.
[0112] Examples of the hydrocarbon type lubricant include
carboxylic acids such as stearic acid and oleic acid; esters such
as butyl stearate; sulfonates such as octadecylsulfonic acid;
phosphates such as monooctadecyl phosphate; alcohols such as
stearyl alcohol and oleyl alcohol; carboxylic acid amides such as
stearic acid amide; and amines such as stearylamine.
[0113] Examples of the fluorine type lubricant include lubricants
obtained by substituting a fluroalkyl group or a perfluoropolyether
group for a part or all of the alkyl group of the aforementioned
hydrocarbon type lubricant.
[0114] Examples of the perfluoropolyether group include
perfluoromethylene oxide polyps, perfluoroethylene oxide polymers,
perfluoro-n-propylene oxide polymers
(CF.sub.2CF.sub.2CF.sub.2O).sub.n, perfluoroisopropylene oxide
polymers (CF(CF.sub.3)CF.sub.2O).sub.n or copolymers of these
compounds. Also, compounds having an polar functional group such as
a hydroxyl group, ester group or carboxyl group at the terminal or
inside thereof have a high effect on a reduction in frictional
force and are therefore preferable. The molecular weight of each of
these compounds is preferably 500 to 5000 and more preferably 1000
to 3000. If the molecular weight less than the above range, there
is the case where the volatility becomes high and the lubricity is
deteriorated. Also, if the molecular weight exceeds the above
range, the viscosity is increased and therefore a slider and a disk
tend to be stuck to each other, causing an operation to be
suspended and head crush.
[0115] Specific examples of the lubricant substituted with
perfluoropolyether include commercially available products under
the name of FOMBLIN from Auzimond and under the name of KRYTOX from
Du Pont K.K.
[0116] Examples of the extreme-pressure type additive include
phosphates such as trilauryl phosphate, phosphites such as
trilauryl phosphite, thiophosphites such as trilauryl
trithiophosphite, thiophosphates and sulfur type e pressure agents
such as dibenzyl disulfide.
[0117] The above lubricants may be used either singly or in
combinations of two or more. As to a method of providing these
lubricants to the magnetic layer or the protective layer, each of
these lubricants may be dissolved in an organic solvent and the
resulting solution may be applied by a wire bar method, gravure
method, spin coating method or dip coating method or deposited by a
vacuum deposition method.
[0118] Examples of the rust preventive agent include
nitrogen-containing heterocyclic compounds such as benzotriazole,
benzimidazole, purine and pyrimidine and derivatives obtained by
introducing an alkyl side chain or the like into each mother
nucleus of these heterocyclic compounds, benzothiazole,
2-mercaptobenzothiazole, tetrazaindene cyclic compounds and
nitrogen- and sulfur-containing heterocyclic compounds such as
thiouracyl compounds and their derivatives.
[0119] In the case of providing a back coat layer (backing layer)
to the surface of the support which is used in the invention and on
which surface no magnetic layer is formed, the back coat layer may
be formed by applying a back coat layer-forming paint obtained by
dispersing particulate components, such as an abrasive material and
an antistatic agent and a binder in an organic solvent, on the
surface of the support on which surface no magnetic layer is
formed.
[0120] As the particulate components, various inorganic pigments
and carbon black may be used. Also, as the binder, resins such as
nitrocellulose, phenoxy resins, vinyl chloride type resins and
polyurethane resins may be used either singly or by mixing these
resins.
[0121] It is to be noted that an adhesive layer may be formed on
the surface of the support to which surface the l ion solution of
the nanoparticle and the back coat layer-forming paint is
applied.
[0122] As a magnetic recording medium for high-density recording,
the magnetic recording medium of the invention preferably has such
a very high smoothness that the center line average roughness of
the surface is in a range from 0.1 to 5 nm and preferably 1 to 4 nm
at a cutoff value of 0.25 mm. In order to make such a surface, it
is preferable to carry out calendering treatment after the magnetic
layer is applied. Also, burnish treatment may be carried out.
[0123] The resulting magnetic recording medium may be used after it
is punched by a punching machine or cut down to a desired size by a
cutter.
EXAMPLES
[0124] The present invention will be explained in detail by way of
examples, which, however, are not intended to be limiting of the
invention. Examples according to the first embodiment of the
invention:
Example 1-1
[0125] The following operations were carried out in high purity
N.sub.2 gas.
[0126] An alkane solution obtained by mixing 10.8 g of Aerosol OT
(manufactured by Wako Pure Chemical Industries, Ltd.), 80 ml of
decane (manufactured by Wako Pure Chemical Industries, Ltd.) and 2
ml of oleylamine (manufactured by Tokyo Kasei Kogyo Co., Ltd.) was
added to and mixed with an aqueous reducing agent solution obtained
by dissolving 0.76 g of NaBH.sub.4 (manufactured by Wako Pure
Chemical Industries, Ltd.) in 16 ml of water (deoxidized: 0.1 mg/l
or less) to prepare an reverse micelle solution (I).
[0127] An alkane solution obtained by mixing 5.4 g of Aerosol OT
and 40 ml of decane was added to and mixed with an aqueous metal
salt solution obtained by dissolving 0.46 g of triammonium iron
trioxalate (Fe(NH.sub.4).sub.3(C.sub.2O.sub.4).sub.3) (manufactured
by Wako Pure Chemical Industries, Ltd.) and 0.38 g of potassium
chloroplatinate (K.sub.2PtCl.sub.4) (manufactured by Wako Pure
Chemical Industries, Ltd.) in 8 ml of water (deoxidized) to prepare
an reverse micelle solution (II).
[0128] The reverse micelle solution (II) was added in an instant to
the reverse micelle solution (I) with stirring the reverse micelle
solution (I) at 22.degree. C. by using an Omni Mixer (manufactured
by Yamato Scientific Co., Ltd.). After ten minutes, the mixture was
raised to 50.degree. C. with stirring by a magnetic stirrer and
then matured for 60 minutes.
[0129] 2 ml of oleic acid (manufactured by Wako Pure Chemical
Industries, Ltd.) was added to the mixture, which was then cooled
to ambient temperature. After cooled, the mixture was taken out in
the atmosphere. In order to destroy reverse micelles, a mixed
solution consisting of 100 ml of water and 100 ml of methanol was
added to the mixture to separate a water phase from an oil phase.
Such a state that nanoparticles were dispersed was obtained in the
oil phase side. The oil phase side was washed with a mixed solution
consisting of 600 ml of H.sub.2O and 200 ml of methanol five
times.
[0130] Thereafter, 1100 ml of methanol was added to the resulting
solution to cause flocculation of the nanoparticles to thereby
precipitate. The supernatant was removed and 20 ml of heptane
(manufactured by Wako Pure Chemical Industries, Ltd.) was added to
redisperse.
[0131] Further, the precipitating operation performed by the
addition of 100 ml of methanol and the dispersing operation using
20 ml of heptane were repeated three times and finally, 5 ml of
heptane was added to the resulting solution to prepare a FePt
nanoparticle dispersion solution in which the ratio
(water/surfactant) by mass of water to a surfactant was 2.
[0132] The yield, composition, volume average particle diameter and
its distribution (coefficient of variation) and coercive force of
the resulting nanoparticles were measured. The results as shown
below were obtained.
[0133] It is to be noted that the composition and the yield were
measured by ICP spectal analysis (inductive coupling high-frequency
plasma spectal analysis).
[0134] The volume average particle diameter and the distribution
were found by measuring particles on a TEM photograph, followed by
statistical processing.
[0135] The coercive force was measured using a high-sensitive
magnetization vector measuring device and a DATA processor
manufactured by Toei Industry Co., Ltd. in the condition of an
applied magnetic field of 790 kA/m (10 kOe). As the nanoparticles
to be subjected to measurement, nanoparticles obtained after
nanoparticles were collected from the prepared nanoparticle
dispersion solution, thoroughly dried and heated in an electric
furnace were used.
[0136] Composition: FePt alloy with 44.5 at % of Pt. yield: 85%
[0137] Avrage particle diameter: 4.2 nm, coefficient of variation:
5%
[0138] Coercive force (550.degree. C. electric furnace, after
heated 30 minutes): 576.7 kA/m (7300 Oe)
Example 1-2
[0139] A FePt nanoparticle dispersion solution in which the ratio
(water/surfactant) by mass of water to a surfactant was 5 was
prepared in the same manner as in Example 1-1 except that the
amount of water in the reverse micelle solution (I) was altered to
40 ml and the amount of water in the reverse micelle solution (II)
was altered to 20 ml.
[0140] The yield, composition, volume average particle diameter and
its distribution (coefficient of variation) and coercive force of
the resulting nanoparticles were measured in the same manner as in
Example 1-1. The results are shown below.
[0141] Composition: FePt alloy with 45.0 at % of Pt, yield: 88%
[0142] Volume average particle diameter. 5.8 nm, coefficient of
variation: 4%
[0143] Coereive force (550.degree. C. electric furnace, after
heated 30 minutes): 521.4 kA/m (6600 Oe)
Example 1-3
[0144] A FePt nanoparticle dispersion solution in which the ratio
(water/surfactant) by mass of water to a surfactant was 8 was
prepared in the same manner as in Example 1-1 except that the
amount of water in the reverse micelle solution (I) was altered to
64 ml and the amount of water in the reverse micelle solution (II)
was altered to 32 ml.
[0145] The yield, composition, volume average particle diameter and
its distribution (coefficient of variation) and coercive force of
the resulting nanoparticles were measured in the same manner as in
Example 1-1. The results are shown below.
[0146] Composition: FePt alloy with 44.8 at % of Pt, yield: 82%
[0147] Volume average particle diameter: 7.6 nm, coefficient of
variation: 4%
[0148] Coercive force (550.degree. C. electric fuinace, after
heated 30 minutes): 417.8 kA/m (5300 Oe)
Example 14
[0149] The following operations were carried out in high purity
N.sub.2 gas.
[0150] An ether solution obtained by mixing 10.8 g of Aerosol OT
(manufactured by Wako Pure Chemical Industries, Ltd.), 80 ml of
dibutyl ether (manufactured by Wako Pure Chemical Industries, lid.)
and 2 ml of oleylamine (manured by Tokyo Kasei Kogyo Co., Ltd.) was
added to and mixed with an aqueous reducing agent solution obtained
by dissolving 0.57 g of NaBH.sub.4 (manufactured by Wako Pure
Chemical Industries, Ltd.) in 16 ml of water (deoxidized: 0.1 mg/l
or less) to prepare an reverse micelle solution (I).
[0151] An ether solution obtained by mixing 5.4 g of Aerosol OT and
40 ml of dibutyl ether was added to and mixed with an aqueous metal
salt solution obtained by dissolving 0.46 g of triammonium iron
trioxalate (Fe(NH.sub.4).sub.3(C.sub.2O.sub.4).sub.3) (manufactured
by Wako Pure Chemical Industries, Ltd.) and 0.32 g of sodium
chloropalladate (Na.sub.2PdCl.sub.4.3H.sub.2O) (manufactured by
Wako Pure Chemical Industries, Ltd.) in 8 ml of water (deoxidized)
to prepare an reverse micelle solution (II).
[0152] The reverse micelle solution (II) was added in an instant to
the reverse micelle solution (I) with string the reverse micelle
solution (I) at 22.degree. C. by using an Omni Mixer (manufactured
by Yamato Scientific Co., Ltd.). After ten minutes, the m e was
raised to 50.degree. C. with stirring by a magnetic stirrer and
then matured for 60 minutes.
[0153] 2 ml of oleic acid (manufactured by Wako Pure Chemical
Industries, Ltd.) was added to the mixture which was then cooled to
ambient temperature. After cooled, the mixture was taken out in the
atmosphere. In order to destroy reverse micelles, a mixed solution
consisting of 100 ml of water and 100 ml of methanol was added to
the mixture to separate a water phase from an oil phase. Such a
state that nanoparticles were dispersed was obtained in the oil
phase side. The oil phase side was washed with a mixed solution
consisting of 600 ml of H.sub.2O and 200 ml of methanol five
times.
[0154] Thereafter, 1100 ml of methanol was added to the resulting
solution to cause flocculation of the nanoparticles to thereby
precipitate. The supernatant was removed and 20 ml of heptane
(manufactured by Wako Pure Chemical Industries, Ltd.) was added to
redisperse.
[0155] Further, the precipitating operation performed by the
addition of 100 ml of methanol and the dispersing operation using
20 ml of heptane were repeated three times and finally, 5 ml of
heptane was added to the resulting solution to prepare a FePd
nanoparticle dispersion solution.
[0156] The yield, composition, volume average particle diameter and
its distribution (coefficient of variation) and coercive force of
the resulting nanoparticles were measured in the same manner as in
Example 1-1. The results are shown below.
[0157] Composition: FePd alloy with 45.2 at % of Pd, yield: 83%
[0158] Volume average particle diameter: 5.6 nm, coefficient of
variation: 4%
[0159] Coercive force (550.degree. C. electric race, after heated
30 minutes): 331.8 kA/m (4200 Oe)
Example 1-5
[0160] A FePtCu nanoparticle dispersion solution was prepared in
the same manner as in Example 1-1 except that an alkane solution
obtained by mixing 5.4 g of Aerosol Or and 40 ml of decane was
added to and mixed with an aqueous metal salt solution obtained by
dissolving 0.39 g of triammonium iron trioxalate
(Fe(NH.sub.4).sub.3(C.sub.2O.sub.4).sub.3) (manufactured by Wako
Pure Chemical Industries, Ltd.), 0.32 g of potassium
chloroplatinate (K.sub.2PtCl.sub.4) (manufactured by Wako Pure
Chemical Industries, Ltd.) and 0.08 g of diammonium copper chloride
(Cu(NH.sub.4).sub.2Cl.sub.4.2H.sub.2O) (manufactured by Wako Pure
Chemical Industries, Ltd.) in 8 ml of water (deoxidized) to prepare
an reverse micelle solution (II).
[0161] The yield, composition, volume average particle diameter and
its distribution (coefficient of variation) and coercive force of
the resulting nanoparticles were measured in the same manner as in
Example 1-1. The results are shown below.
[0162] Composition: FePtCu alloy with 38.5 at % of Pt and 14.6 at %
of Cu, yield: 88%
[0163] Volume average particle diameter: 4.4 nm, coefficient of
varation: 5%
[0164] Coercieve force (250.degree. C. electric furnace, after
heated 30 minutes): 371.3 kA/m (4700 Oe)
[0165] Coercive force (550.degree. C. electric furnace, after
heated 30 minutes): 497.7 kA/m (6300 Oe)
Comparative Example 1-1
[0166] A FePt nanoparticle dispersion solution was prepared in the
same manner as in Example 1-1 except that the reverse micelle
solution (I) was mixed with the reverse micelle solution (II) at
ambient temperature (about 25.degree. C.), the reducing reaction
was run with stirring using a magnetic stirrer and the reaction
mixture was matured at the same temperature (25.degree. C.) for 120
minutes.
[0167] The yield, composition, volume average particle diameter and
its distribution (coefficient of variation) and coercive force of
the resulting nanoparticles were measured in the same manner as in
Example 1-1. The results are shown below.
[0168] Composition: FePt alloy with 23.1 at % of Pt, yield: 25%
[0169] Volume average particle diameter: 3.9 nm, coefficient of
variation: 33%
[0170] Coercive force (550.degree. C. electric flrnace, after
heated 30 minutes): 49.77 kA/m (630 Oe)
Comparative Example 1-2
[0171] A FePt nanoparticle dispersion solution was prepared in the
same manner as in Example 1-1 except that the reverse micelle
solution (I) was reacted with the reverse micelle solution (II) at
60.degree. C. with string using a magnetic stirrer and the reaction
mixture was matured at the same temperature for 20 minutes.
[0172] The yield, composition, volume average particle diameter and
its distribution (coefficient of variation) and coercive force of
the resulting nanoparticles were measured in the same manner as in
Example 1-1. The results are shown below.
[0173] Composition: FePt alloy with 52.0 at % of Pt, yield: 19%
[0174] Volume avenge partcle diamee: 4.8 mn, coefficient of
variation: 41%
[0175] Coercive force (550.degree. C. electric furnace, after
heated 30 minutes): 120.08 kA/m (1520 Oe)
Comparative Example 1-3
[0176] A FePt nanoparticle dispersion solution was prepared in the
same manner as in Example 1-1 except that a reducing reaction was
run between the reverse micelle solution (I) and the reverse
micelle solution (II) at ambient temperature (about 25.degree. C.)
with stirring using a magnetic stiffer such that the ratio by mass
of water to a surfactant was 30 and after 10 minutes, the reaction
mixture was matured at 50.degree. C. for 60 minutes.
[0177] The yield, composition, volume average particle diameter and
its distribution (coefficient of variation) and coercive force of
the resulting nanoparticles were measured in the same manner as in
Example 1-1. The results are shown below.
[0178] Composition: FePt alloy with 47.2 at % of Pt, yield: 45%
[0179] Volume average particle diameter. 4.1 nm, coefficient of
varation: 30%
[0180] Coercive force (550.degree. C. electric ftace, after heated
30 minutes): 153.26 kA/m (1940 Oe)
[0181] In the case of the aforementioned nanoparticles of Examples
1 to 5 as compared with Comparative Examples 1 to 3, compositions
close to those according to the formulation were obtained in a high
yield. It was also clarified that the nanoparticles of Examples 1
to 5 had such superiority that these nanoparticles were reduced in
the coefficient of variation as to the distribution of particle
diameter, showing that they were monodispersions and had a high
coercive force after heated.
[0182] The nanoparticle dispersion solutions prepared in Examples 1
to 5 and Comparative Examples 1 to 3 wee respectively applied to
the sputtered surface of a glass substrate (support), on which a
200-nm-thick layer made of carbon was formed by sputtering, by a
spin coating method. The coating amounts were each made to be 0.4
g/m.sup.2.
[0183] After coated, each glass substrate was subjected to
annealing treatment performed in an electric furnace (500.degree.
C., 30 minutes) to produce a magnetic recording medium (thickness
of the magnetic layer: 40 nm). The glass substrate to which the
nanoparticle dispersion solution prepared in Example 1-5 was
separately applied was subjected to annealing treatment performed
at 250.degree. C. for 30 minutes to produce a magnetic recording
medium.
[0184] The coercive force (Hc) of each of the produced magnetic
recording media was measured using a high-sensitive magnetization
vector measuring device and a DATA processor manufactured by Toei
Industry Co., Ltd. in the condition of an applied magnetic field of
790 kA/m (10 kOe).
[0185] The results are shown in Table 1.
1 TABLE 1 Annealing temperature Coercive force (Hc) Example 1-1
500.degree. C. 442.4 kA/m (5600 (Oe)) Example 1-2 500.degree. C.
402.9 kA(m (5100 (Oe)) Example 1-3 500.degree. C. 387.1 kA/m (4900
(Oe)) Example 1-4 500.degree. C. 276.5 kA/m (3500 (Oe)) Example 1-5
250.degree. C. 308.1 kA/m (3900 (Oe)) 500.degree. C. 371.3 kA/m
(4700 (0e)) Comparative Example 1-1 500.degree. C. 14.22 kA/m (180
(Oe)) Comparative Example 1-2 500.degree. C. 45.82 kA/m (580 (Oe))
Comparative Example 1-3 500.degree. C. 86.9 kA/m (1100 (Oe))
[0186] As is clear from Table 1, it was confirmed that the metal
nanoparticle (Examples 1-1 to 1-5) of the invention had a high
coercive force even if it was heat-treated in a coated state.
[0187] As aforementioned, the invention can provide nanoparticles
which are scarcely coagulated with each other and have superior
coatability and of which the size and composition can be controlled
and a method of producing the nanoparticles. Also, the invention
can provide a magnetic recording medium exhibiting hard magnetism
by compounding a nanoparticle in a magnetic layer. Examples
according to the second embodiment of the invention:
Example 2-1
[0188] The following operations were carried out in high purity
N.sub.2 gas.
[0189] An alkane solution obtained by dissolving 10.8 g of Aerosol
OT in 80 ml of decane was added to and mixed with an aqueous metal
salt solution obtained by dissolving 0.35 g of triammonium iron
trioxalate (Fe(NH.sub.4).sub.3(C.sub.2O.sub.4).sub.3) (manufactured
by Wako Pure Chemical Industries, Ltd.) and 0.35 g of potassium
chloroplatinate (K.sub.2PtCl.sub.4) (manufactured by Wako Pure
Chemical Industries, IL) in 24 ml of water (deoxidized) to prepare
an reverse micelle solution (I.sub.a)
[0190] An alkane solution obtained by dissolving 5.4 g of Aerosol
OT (manufactured by Wako Pure Chemical Industries, Ltd.) and 2 ml
of oleylamine (manufactured by Tokyo Kasei Kogyo Co., Ltd.) in 40
ml of decane (manufactured by Wako Pure Chemical Industries, Ltd.)
was added to and mixed with an aqueous reducing agent solution
obtained by dissolving 0.57 g of NaBH.sub.4 (manufactured by Wako
Pure Chemical Industries, Ltd.) in 12 ml of H.sub.2O (deoxidized)
to prepare an reverse micelle solution (II.sub.a).
[0191] An alkane solution obtained by dissolving 2.7 g of Aerosol
OT in 20 ml of decane was added to and i d with an aqueous metal
salt solution obtained by dissolving 0.07 g of copper chloride
(CuCl.sub.2.6H.sub.2O) (manufactured by Wako Pure Chemical
Industries, Ltd.) in 2 ml of H.sub.2O (deoxidized) to prepare an
reverse micelle solution (I.sub.b).
[0192] An alkane solution obtained by dissolving 5.4 g of Aerosol
OT (manufactured by Wako Pure Chemical Industries, Ltd.) in 40 ml
of decane (manufactured by Wako Pure Chemical Industries, Ltd.) was
added to and mixed with an aqueous reducing agent solution obtained
by dissolving 0.88 g of ascorbic acid (manufactured by Wako Pure
Chemical Industries, Ltd.) in 12 ml of water (deoxidized) to
prepare an reverse micelle solution (II.sub.b).
[0193] The reverse micelle solution (II.sub.a) was added in an
instant to the reverse micelle solution (I.sub.a) with siring the
reverse micelle solution (I.sub.a) at a high rate at 22.degree. C.
by using an Omni Mixer (manufactured by Yamato Scientific Co.,
Ltd.). After 3 minutes, the reverse micelle solution (I.sub.b) was
further added over about 10 minutes at a rate of about 2.4 ml/min.
The stirring was changed to one using a magnetic stirrer 5 minutes
after the addition was finished and the mixture was raised to
40.degree. C. Then, the reverse micelle solution (II.sub.b) was
added and the mire was matured for 120 minutes.
[0194] After the mixture was cooled to ambient temperature, 2 ml of
oleic acid (manufactured by Wako Pure Chemical Industries, Ltd.)
was added to and mixed with the be, which was then taken out in the
atmosphere. In order to destroy reverse micelles, a mixed solution
consisting of 200 ml of H.sub.2O and 200 ml of methanol was added
to the mixture to separate a water phase from an oil phase. Such a
state that metal nanoparticles were dispersed was obtained in the
oil phase side. The oil phase side was washed with a mixed solution
consisting of 600 ml of H.sub.2O and 200 ml of methanol five tunes.
Thereafter, 1300 ml of methanol was added to the resulting solution
to cause flocculation of the metal nanoparticles to thereby
precipitate. The supernatant was removed and 20 ml of heptane
(manufactured by Wako Pure, Chemical Industries, Ltd.) was added to
redisperse. Further, the precipitating operation performed by the
addition of 100 ml of methanol and the dispersing operation using
20 ml of heptane were repeated twice and finally, 5 ml of octane
(manufactured by Wako Pure Chemical Industries, Ltd.) was added to
the resulting solution to prepare a FeCuPt nanoparticle dispersion
solution.
Example 2-2
[0195] A FeInPt nanoparticle dispersion solution was obtained in
the same manner as in Example 2-1 except that the metal salt in the
reverse micelle solution (I.sub.b) was altered to 0.07 g of
InCl.sub.3 (manufactured by Wako Pure Chemical Industries, Ltd.) in
Example 2-1.
Example 2-3
[0196] A FePbPt nanoparticle dispersion solution was obtained in
the same manner as in Example 2-1 except that the metal salt in the
reverse micelle solution (I.sub.b) was altered to 0.08 g of
PbCl.sub.2 (manufactured by Wako Pure Chemical Industries, Ltd.) in
Example 2-1.
Example 2-4
[0197] A CoBiPt nanoparticle dispersion solution was obtained in
the same manner as in Example 2-1 except that the metal salts used
in the reverse micelle solutions (I.sub.a) and (I.sub.b) were
altered to the following ones in Example 2-1.
[0198] Metal salt in the reverse micelle solution (I.sub.a): 0.20 g
of cobalt chloride (CoCl.sub.2.6H.sub.2O) and 0.35 g of potassium
chloroplatinate (K.sub.2PtCl.sub.4) (manufactured by Wako Pure
Chemical Industries, Ltd.)
[0199] Metal salt of the reverse micelle solution (I.sub.b): 0.41 g
of bismuth nitrate (Bi(NO.sub.3).sub.3.5H.sub.2O)
Example 2-5
[0200] The following operations were carried out in high purity
N.sub.2 gas.
[0201] An alkane solution obtained by dissolving 10.8 g of Aerosol
OT in 80 ml of decane was added to and mixed with an aqueous metal
salt solution obtained by dissolving 0.18 g of t onium iron
trioxalate (Fe(NH.sub.4).sub.3(C.sub.2O.sub.4).sub.3) (manufactured
by Wako Pure Chemical Industries, Ltd.) and 0.35 g of potassium
chloroplatinate (K.sub.2PtCl.sub.4) (manufactured by Wako Pure
Chemical Industries, Ltd.) in 24 ml of H.sub.2O (deoxidized) to
prepare an reverse micelle solution (I.sub.a).
[0202] An alkane solution obtained by dissolving 2.7 g of Aerosol
OT in 20 ml of decane was added to and mixed with an aqueous metal
salt solution obtained by dissolving 0.10 g of cobalt chloride
(CoCl.sub.2.6H.sub.2O) (manufactured by Wako Pure Chemical
Industries, Ltd.) in 2 ml of H.sub.2O (deoxidized) to prepare an
reverse micelle solution (I.sub.b).
[0203] An alkane solution obtained by dissolving 5.4 g of Aerosol
OT (manufactured by Wako Pure Chemical Industries, Ltd.) and 2 ml
of oleylamine (manufactured by Tokyo Kasei Kogyo Co., Ltd.) in 40
ml of decane (manufactured by Wako Pure Chemical Industries, Ltd.)
was added to and mixed with an aqueous reducing agent solution
obtained by dissolving 0.57 g of NaBH.sub.4 (manufactured by Wako
Pure Chemical Industries, Ltd.) in 12 ml of H.sub.2O (deoxidized)
to prepare an reverse micelle solution (II.sub.a).
[0204] An alkane solution obtained by dissolving 2.7 g of Aerosol
OT in 20 ml of decane was added to and mixed with an aqueous metal
salt solution obtained by dissolving 0.06 g of copper acetate
(Cu(CH.sub.3COO).sub.2H.s- ub.2O) (manufactured by Wako Pure
Chemical Industries, Ltd.) in 2 ml of H.sub.2O (deoxidized) to
prepare an reverse micelle solution (I.sub.c).
[0205] An alkane solution obtained by dissolving 5.4 g of Aerosol
OT (manufactured by Wako Pure Chemical Industries, Ltd.) in 40 ml
of decane (manufactured by Wako Pure Chemical Industries, Ltd.) was
added to and mixed with an aqueous reducing agent solution obtained
by dissolving 0.88 g of ascorbic acid (manufactured by Wako Pure
Chemical Industries, Ltd.) in 12 ml of H.sub.2O (deoxidized) to
prepare an reverse micelle solution (II.sub.b).
[0206] The reverse micelle solution (I.sub.b) was added in an
instant to the reverse micelle solution (I) with stirring the
reverse micelle solution (I) at a high rate at 22.degree. C. by
using an Omni Mixer (manufactured by Yamato Scientific Co., Ltd.).
After 2 minutes, the reverse micelle solution (II.sub.a) was
further added in an instant. After three minutes, the reverse
micelle solution (I.sub.c) was further added over about 10 minutes
at a rate of about 24 ml/min. The stirring was changed to one using
a magnetic stirrer 5 minutes after the addition was finished and
the mixture was raised to 40.degree. C. Then, the reverse micelle
solution (II.sub.b) was added and the mixture was matured for 120
minutes.
[0207] The same washing and refining were carried out in the same
manner as in Example 2-1 to obtain a FeCoCuPt nanoparticle
dispersion solution.
Example 2-6
[0208] A FeCoInPt nanoparticle dispersion solution was obtained in
the same manner as in Example 2-5 except that 0.33 g of a chelating
agent (DHEG) was added to each of the reverse micelle solutions
(I.sub.a) and (I.sub.b) and the metal salt of the reverse micelle
solution (I.sub.b) was altered to 0.07 g of InCl.sub.3
(manufactured by Wako Pure Chemical Industries, Ltd.).
Comparative Example 2-1
[0209] A FePt nanoparticle dispersion solution was obtained in the
same manner as in Example 2-1 except that the reverse micelle
solutions (I.sub.b) and (II.sub.b) were not used, and the reverse
micelle solution (II.sub.a) was added in an instant to the reverse
micelle solution (I) at ambient temperature (25.degree. C.) with
siring the reverse micelle solution (I) by using a magnetic stirrer
to cause a reducing reaction and the mixture was mated at the same
temperature for 120 minutes.
Comparative Example 2-2
[0210] In Example 2-1, the reverse micelle solution (I.sub.b) was
not used and the reverse micelle solution (II.sub.a) was added in
an instant to the reverse micelle solution (I.sub.a) at 22.degree.
C. with stirring the reverse micelle solution (I.sub.a) at a high
rate using an Omni Mixer (manufactured by Yamato Scientific Co.,
Ltd.). The stirring was altered to one using a magnetic stirrer
after 10 minutes, the mixture was raised to 40.degree. C. and the
reverse micelle solution (II.sub.b) was then added to the mid=,
which was then matured for 120 minutes. The same procedures as in
Example 2-1 except for the above procedures were conducted to
obtain a FePt nanoparticle dispersion solution.
Comparative Example 2-3
[0211] The following procedures were conducted in high purity
N.sub.2 gas.
[0212] 0.39 g of platinum acetylacetonate (Pt(acac).sub.2)
(manufactured by Wako Pure Chemical Industries, Ltd.), 0.6 ml of
1,12-dodecandiol (manufactured by Wako Pure Chemical Industries,
Ltd.) and 20 ml of dioctyl ether were mixed with each other and the
mixture was heated up to 100.degree. C. Thereafter, 0.28 ml of
oleic acid, 0.26 ml of oleylamine and 0.25 g of ion acetylacetonate
(Fe(acac).sub.3) were added. The mixture was raised up to
297.degree. C. and then refluxed for 30 minutes.
[0213] After the mixture was cooled, 200 ml of methanol was added
to cause the metal nanoparticle to flocculated and to precipitate.
After the supernatant was removed, 20 ml of heptane was added to
the precipitate to redisperse. 100 ml of methanol was added again
to precipitate. The dispersion using heptane and the precipitation
using methanol were repeated once more and then the nanoparticles
were dispersed using 5 ml of octane to obtain a FePt nanoparticle
dispersion solution.
[0214] The nanoparticles obtained in Examples 2-1 to 2-6 and
Comparative Examples 1 to 3 were analyzed to obtain the results
shown in Table 2.
[0215] In Table 2, the composition and the yield were measured by
ICP spectral analysis (inductive coupling high-frequency plasma
spectral analysis) after the dispersion solution was evaporated to
dryness, organic substances were decomposed using strong sulfuric
acid and then the resulting product was dissolved in aqua
regia.
[0216] The number average particle diamond and the distribution
were calculated by measuring particles on a TEM photograph,
followed by statistical processing.
[0217] The coercive force was measured using a high-sensitive
magnetization vector measuring device and a DATA processor
manufactured by Toei Industry Co., Ltd. in the condition of an
applied magnetic field of 790 kA/m (10 kOe). As the nanoparticles
to be subjected to measurement, nanoparticles were used which were
obtained after the nanoparticle dispersion solution was evaporated
to dryness and then annealed (550.degree. C. or 350.degree. C.) in
an Ar mixture gas containing 5% of H.sub.2 in an infrared heating
furnace (manufactured by ULVAC-RIKO, Inc.).
2 TABLE 2 Number average Elemental Composition ratio particle
Coefficient of Coercive force Coercive force structure of of
nanoparticles Yield diameter variation after annealed at after
annealed at nanoparticles (at. %) (%) (nm) (%) 550.degree. C.
(KA/m) 350.degree. C. (KA/m) Example 2-1 Fe/Cu/Pt 42/16/42 80 5.1 5
501.4 397.9 Example 2-2 Fe/In/Pt 44/14/42 83 5.5 5 541.2 437.7
Example 2-3 Fe/Pb/Pt 40/17/43 79 5.4 6 477.5 390.0 Example 2-4
Co/Bi/Pt 43/15/42 82 5.0 7 461.6 358.1 Example 2-5 Fe/Co/Cu/Pt
20/22/15/43 80 5.2 6 525.3 405.9 Example 2-6 Fe/Co/In/Pt
21/20/16/43 82 5.5 6 557.1 421.8 Comparative Fe/Pt 75/25 26 4.1 31
62.1 4.0 Example 2-1 Comparative Fe/Pt 51/49 80 5.0 6 549.1 15.9
Example 2-2 Comparative Fe/Pt 57/43 58 4.9 26 310.4 5.6 Example
2-3
[0218] As is clear from Table 2, a composition close to that of the
formulation was obtained in a higher yield in the case of each
nanoparticle of Examples 2-1 to 2-6 than in the case of each
nanoparticle of Comparative Example 2-1 to 2-3. Also, the
nanoparticles of Examples 2-1 to 2-6 were reduced in the
coefficient of variation in the distribution of particle diameters,
showing that these nanoparticles were monodispersions, and had high
coercive force after annealing. Further, the nanoparticles of
Examples 2-1 to 2-6 exhibited higher coercive force than those of
Comparative Examples 1 to 3 also when performing annealing
treatment at low temperature (350.degree. C.).
[0219] Each nanoparticle dispersion solution prepared in Examples
2-1 to 2-6 and Comparative Examples 2-1 to 2-3 was applied to a
fired Si substrate (a 300-nm-thick SiO.sub.2 layer was formed on
the surface of Si) by a spin coating method. The amount of each
solution to be applied was made to be 0.1 g/m.sup.2.
[0220] After applied, each coated sample was annealed at
350.degree. C. for 30 minutes using Ar+H.sub.2(5%) mitre gas in an
inredheating furnace (manufactured by ULVAC-RIKO, Inc.) to form a
magnetic layer on the substrate.
[0221] After the annealing treatment, a carbon layer 10 nm in
thickness was applied to the surface of the magnetic layer by a
sputtering apparatus (manufactured by Shibaura Mechatronics
Corporation) and a lubricant (FOMBLIN, manufactured by AUSIMONT)
was applied to the carbon layer in a thickness of about 5 nm by a
spin coating method to make a magnetic recording medium.
[0222] The magnetic characteristics of each sample were evaluated.
As a result, each of Comparative Examples 2-1 to 2-3 exhibited no
hard magnetism whereas each of Examples 2-1 to 2-6 had a coercive
force of 318.3 KA/m (4000 Oe) or more, exhibiting hard
magnetism.
[0223] Also, the nanoparticles of each of Examples 2-1 to 2-6 were
not fused among them by an annealing treatment but maintained the
particle diameter which each had before the annealing
treatment.
[0224] As aforementioned, the method of producing a nanoparticle
according to the present invention can produce a nanoparticle which
has a low transformation temperature, Is scarcely coagulated, has
high coatability, possesses a controllable size and composition and
can develop ferromagnetism in a high yield.
* * * * *