U.S. patent application number 11/475013 was filed with the patent office on 2006-11-02 for method for producing nanoparticle layer having uniform easy axis of magnetization, magnetic recording medium having such layer, its production method, and its production apparatus.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Motoyasu Terao, Yuko Tsuchiya.
Application Number | 20060246227 11/475013 |
Document ID | / |
Family ID | 32709012 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060246227 |
Kind Code |
A1 |
Tsuchiya; Yuko ; et
al. |
November 2, 2006 |
Method for producing nanoparticle layer having uniform easy axis of
magnetization, magnetic recording medium having such layer, its
production method, and its production apparatus
Abstract
The magnetic recording medium provided is produced by forming a
substrate having a nanoparticle layer comprising an array of
nanoparticles, and an organic compound between said array of
nanoparticles; irradiating the nanoparticle layer with an infrared
beam to magnetize the nanoparticles; applying a magnetic field to
the nanoparticle layer to orient easy axis of magnetization of the
magnetic nanoparticles in a substantially uniform direction; and
irradiating the nanoparticle layer with an ultraviolet beam to bind
said organic compound to thereby produce a magnetic recording
medium wherein easy axis of magnetization of the nanoparticles has
been oriented in a direction substantially parallel to a direction
at a particular angle with the substrate. The resulting magnetic
recording medium experiences no deterioration of the underlying
layer or the soft magnetic layer, and exhibits good magnetic
properties.
Inventors: |
Tsuchiya; Yuko; (Tokorozawa,
JP) ; Terao; Motoyasu; (Hinode, JP) |
Correspondence
Address: |
Stanley P. Fisher;Reed Smith LLP
Suite 1400
3110 Fairview Park Drive
Falls Church
VA
22042-4503
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
32709012 |
Appl. No.: |
11/475013 |
Filed: |
June 27, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10750882 |
Jan 5, 2004 |
|
|
|
11475013 |
Jun 27, 2006 |
|
|
|
Current U.S.
Class: |
427/548 ;
427/127; G9B/5; G9B/5.238; G9B/5.295; G9B/5.305 |
Current CPC
Class: |
G11B 5/65 20130101; G11B
5/00 20130101; G11B 11/10536 20130101; G11B 5/84 20130101; G11B
2005/0005 20130101; Y10T 428/256 20150115; G11B 2005/0002 20130101;
G11B 5/82 20130101; G11B 5/852 20130101; G11B 2005/0021 20130101;
G11B 5/012 20130101 |
Class at
Publication: |
427/548 ;
427/127 |
International
Class: |
H01F 1/00 20060101
H01F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 14, 2003 |
JP |
2003-005242 |
Claims
1. A method for producing a magnetic recording medium comprising:
forming a nanoparticle layer on a substrate having a surface, or on
an underlying layer or a soft magnetic layer formed on said
substrate by arranging particles in a substantially ordered array,
forming the nanoparticles by making each of said particles comprise
a nanoparticle and an organic compound coating said nanoparticle,
wherein said nanoparticles having an average particle size of at
least 1 nm and not more than 20 nm, and containing at least one
element selected from the group consisting of Fe, Co, Ni, Mn, Sm,
Pt, and Pd; irradiating said nanoparticle layer with an infrared
beam to magnetize said nanoparticles and produce magnetic
nanoparticles; applying a magnetic field to said nanoparticle layer
to orient an easy axis of magnetization of said magnetic
nanoparticles in a substantially uniform direction; and irradiating
said nanoparticle layer with an ultraviolet beam to bind said
organic compound.
2. A method for producing a magnetic recording medium according to
claim 1 wherein said step of forming the nanoparticle layer is
accomplished by employing a Langmuir-Blodgett method wherein a
colloid solution of the nanoparticles coated with the organic
compound is added dropwise onto a water surface to form a monolayer
film, and the thus formed film is compressed to obtain a film
wherein nanoparticles are densely arranged.
3. A method for producing a magnetic recording medium according to
claim 1 wherein said step of forming the nanoparticle layer is
accomplished by employing spin coating wherein a colloid solution
of the nanoparticles coated with the organic compound is added
dropwise onto the substrate and the substrate is rotated to form a
thin film.
4. A method for producing a magnetic recording medium according to
claim 1 wherein said infrared beam has a wavelength longer than 600
nm.
5. A method for producing a magnetic recording medium according to
claim 1 wherein said ultraviolet beam has a wavelength shorter than
400 nm.
6. A method for producing a magnetic recording medium according to
claim 1 wherein said infrared beam or said ultraviolet beam used,
is a laser beam.
7. A method for producing a magnetic recording medium according to
claim 1 wherein said magnetic field is a static magnetic field
wherein direction and intensity of the magnetic field do not change
with time.
8. A method for producing a magnetic recording medium according to
claim 1 wherein when applying a magnetic field, said magnetic field
is a pulse magnetic field wherein direction of the magnetic field
applied is constant, and intensity of the magnetic field varies
with time.
9. A method for producing a magnetic recording medium according to
claim 1 wherein the magnetic field is applied in a direction
substantially parallel to said substrate surface.
10. A method for producing a magnetic recording medium according to
claim 1 wherein the magnetic field is applied in a direction which
is substantially parallel to a direction at 45 degrees to said
substrate surface.
11. A method for producing a magnetic recording medium according to
claim 1 wherein the magnetic field is applied in a direction
substantially parallel to a direction which is perpendicular to
said substrate surface.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional application of U.S.
application Ser. No. 10/750,882 filed Jan. 5, 2004. Priority is
claimed based on U.S. application Ser. No. 10/750,882 filed Jan. 5,
2004, which claims the priority of Japanese Patent Application No.
2003-005242 filed Jan. 14, 2003, all of which is incorporated by
reference.
FIELD OF THE INVENTION
[0002] This invention relates to a magnetic, a thermomagnetic, or a
magnetooptical recording medium used in a magnetic disk system or
the like, a method for recording using such magnetic recording
medium, and an apparatus for producing such magnetic recording
medium.
BACKGROUND OF THE INVENTION
[0003] With the recent increase in the capacity of the magnetic
recording system, attempts have been made to increase recording
density of the magnetic recording medium. In order to increase the
density of the recording bit on the magnetic recording medium,
decrease in the noise of the medium is necessary, and for this, use
of smaller magnetization reversal units on the magnetic recording
layer is required. Reduction in the size of the magnetic crystal
grains constituting the magnetic recording layer has been found
effective for such increase in the recording density. However, use
of excessively minute magnetic crystal grains is known to invite
thermal demagnetization wherein magnetization on the magnetic
recording layer becomes thermally unstable. Use of magnetic crystal
grains having a uniform size distribution is important to reduce
the thermal demagnetization. In other words, size reduction of the
magnetic crystal grains simultaneously with the reduction in the
grain size dispersion or standard deviation is required in the
medium adapted for use in high density recording.
[0004] Conventional magnetic recording mediums have been produced
by sputtering a seed layer, an underlying layer, a magnetic layer
functioning as a recording layer, a protective layer, and the like
in this order on a circular glass or aluminum substrate. In the
magnetic layer formed by sputtering, size dispersion of the
magnetic crystal grains constituting the magnetic layer is large.
The size dispersion and the average grain size, however, can be
reduced in the case of sputtering by controlling the conditions of
the film deposition. Still, the control of the grain size
dispersion is difficult, and it is said that the grain size
dispersion is limited to the level of about 20%.
[0005] An attempt to overcome the need for reducing the size and
size dispersion degree of the magnetic crystal grains is disclosed
in Patent Document 1, (Japanese Patent Laid-Open No. 2000-48340,
corresponding to U.S. Pat. No. 6,162,532) and a document relevant
to this Patent Document 1, is Non-Patent Document 1, Science, vol.
287, pages 1989 to 1992 (issue of Mar. 17, 2000).
[0006] In Patent Document 1 and Non-Patent Document 1, the magnetic
nanoparticles constituting the recording layer are produced not by
the conventional sputtering but by a chemical synthesis. In
Non-Patent Document 1, FePt alloy (uniaxial anisotropy constant,
Ku: 7.times.10.sup.6 J/m.sup.3) which is a hopeful candidate for
the near future high recording density is synthesized in an organic
solvent by reacting an iron pentacarbonyl compound (Fe(CO).sub.5)
and an acetylacetone platinum compound (Pt(acac).sub.2). According
to the Patent Document 1 and the Non-Patent Document 1, magnetic
nanoparticles having an arbitrary diameter in the range of at least
3 nm and up to 10 nm with the size dispersion standard deviation of
5 to 10% could be selectively produced by using the chemical
synthesis as described above.
[0007] The magnetic nanoparticle produced by the chemical
sysnthesis as described in the Patent Document 1 and the Non-Patent
Document 1 comprises a magnetic metal as indicated 1 in FIG. 1,
which comprises either a single magnetic metal element or an alloy
containing at least one magnetic metal element. Such magnetic
nanoparticle is coated with an organic compound as indicated by 2.
This coating of the organic compound improves adhesion both between
the magnetic nanoparticles and the substrate surface and between
the adjacent magnetic nanoparticles, and there is disclosed that
such organic compound coating facilitates the stable production of
the ordered array of the magnetic nanoparticles in the formation of
the monolayer or multilayer film. FIG. 2 shows a monolayer film of
magnetic nanoparticles. In FIG. 2(a), the layer of magnetic
nanoparticle layer 5 is formed on the underlying layer or the soft
magnetic layer 4 formed on the substrate 3, and the magnetic
nanoparticle 1 is covered with the coating 2.
[0008] In addition to the role as described above, the coating of
the organic compound is believed to play an important role of
improving the storage stability of the colloid solution of the
magnetic nanoparticles. The presence of the organic compound
coating between the magnetic nanoparticles in the resulting film is
also believed to reduce the magnetic interaction between the
adjacent magnetic nanoparticles. This phenomenon may be similar to
the phenomenon found in the medium having the layer of CoCrPt,
CoCrTa, or the like formed by sputtering wherein Cr segregated
layer is formed at the boundary of the magnetic crystal grains.
[0009] Typical organic compounds used for the coating in the Patent
Document 1 are organic materials containing a long chain organic
compound represented by the formula: R--X wherein R is desirably a
member selected from straight and branched hydrocarbon and
fluorocarbon chains containing 6 to 22 carbon atoms, and X is
desirably a member selected from carboxylic acids, phosphonic
acids, phosphinic acids, sulfonic acids, sulfinic acids, and
thiols, among which oleic acid being mentioned as the most
desirable for use as the coating.
[0010] Non-Patent Document 1 describes that, when the recording
layer comprising magnetic nanoparticles formed was subjected to a
high temperature heat treatment at about 560.degree. C., the
coating of the organic compound such as oleic acid did not
evaporate, but became carbonized as indicated by 6 in FIG. 2(b) and
remained around the magnetic nanoparticles. Such carbonized organic
substance remaining between the magnetic nanoparticles is believed
to contribute for the reduction of the magnetic interaction between
the magnetic particles. Non-Patent Document 1 also describes that
crystallographic structure of the FePt magnetic nanoparticles
changes by the heat treatment from the fcc structure at the time of
its chemical sysnthesis into the ordered structure L10. In the case
of FePt, magnetism is not found in the fcc structure, and
ferromagnetism is developed when it takes the ordered structure. It
is to be noted that the magnetic field was not applied in the heat
treatment after the film formation. Accordingly, the easy axis of
magnetization of the magnetic nanoparticles is believed to be
randomly oriented.
[0011] In the technology described in Non-Patent Document 1, the
nanoparticle layer formed is subjected to a high temperature
treatment at about 500.degree. C. to 600.degree. C. to thereby
convert the nanoparticle crystal structure from fcc structure to
L10 ordered structure to thereby magnetize the nanoparticles to the
degree sufficient for use as a recording medium. As a result of
such high temperature heat treatment, the nanoparticle layer
experiences disturbance in the array of the nanoparticles as well
as agglomeration of the nanoparticles, and when such nanoparticle
layer is used in a magnetic recording layer, the layer suffers from
an insufficient flatness. The high temperature heat treatment also
results in the undesirable deterioration of the underlying layer,
the soft magnetic layer, and the like between the nanoparticle
layer and the substrate. In spite of the high magnetization degree
of the nanoparticle layer after the high temperature heat
treatment, it is difficult to use such nanoparticle layer in a
magnetic recording medium wherein the substrate is actually rotated
for the reading and writing of the information by the read
head.
[0012] On the other hand, in the technology described in Patent
Document 1, the easy axis of magnetization of the magnetic
nanoparticles constituting the recording layer is randomly
oriented, and orientation of the easy axis of magnetization in a
particular direction such as in-plane direction of the medium or
thickness direction of the medium is difficult. As a consequence of
such difficulty, the resulting magnetic recording layer suffers
from inferior magnetic properties compared to the conventional
in-plane recording or perpendicular recording medium.
SUMMARY OF THE INVENTION
[0013] In view of the situation as described above, the present
invention may include providing a magnetic recording medium having
a nanoparticle layer wherein the high temperature heat treatment
that had been conducted for magnetization of the nanoparticles is
no longer necessary, flatness of nanoparticle layer has been
improved, the underlying layer and the soft magnetic layer do not
experience deterioration, easy axis of magnetization of the
nanoparticles is substantially parallel to a direction which is at
a particular angle to said substrate surface, and excellent
magnetic properties are realized. Other features of the invention
may include to providing a method for producing such medium and
apparatus used in producing such medium.
[0014] The features as described above are attained by using a
magnetic recording medium at least comprising a substrate having a
surface; and a nanoparticle layer comprising an array of
nanoparticles having an average particle size of at least 1 nm and
not more than 20 nm, and containing at least one element selected
from Fe, Co, Ni, Mn, Sm, Pt, and Pd, and an organic compound
between said array of nanoparticles; wherein easy axis of
magnetization of said nanoparticles is substantially parallel to a
direction which is at a particular angle to said substrate surface.
Such magnetic recording medium can be produced by a method for
producing a magnetic recording medium comprising the steps of:
forming a nanoparticle layer on a substrate having a surface or on
an underlying layer or a soft magnetic layer formed on said
substrate by arranging particles in a substantially ordered array,
said particles each comprising a nanoparticle and an organic
compound coating said nanoparticle, and said nanoparticles having
an average particle size of at least 1 nm and not more than 20 nm,
and containing at least one element selected from Fe, Co, Ni, Mn,
Sm, Pt, and Pd; irradiating said nanoparticle layer with an
infrared beam to magnetize said nanoparticles and produce magnetic
nanoparticles; applying a magnetic field to said nanoparticle layer
to orient easy axis of magnetization of said magnetic nanoparticles
in a substantially uniform direction; and irradiating said
nanoparticle layer with an ultraviolet beam to bind said organic
compound. In addition, such magnetic recording medium can be
produce by an apparatus having an infrared irradiating section for
irradiating a particular region of the substrate having the
nanoparticle layer formed thereon with an infrared beam; a magnetic
field applying section for applying a magnetic field to said
particular region after the irradiation of the infrared beam; and
an ultraviolet irradiating section for irradiating said particular
region with an ultraviolet beam after the application of the
magnetic field.
BRIEF DESCRIPTION OF THE DRAWING
[0015] FIG. 1 is a view showing prior art nanoparticles covered
with a coating;
[0016] FIGS. 2A-2B are prior art cross-sectional views of the
magnetic recording medium having a nanoparticle layer;
[0017] FIG. 3A-3B are views showing an apparatus for producing the
magnetic recording medium having a nanoparticle layer wherein the
easy axis of magnetization of nanoparticles is oriented in the same
direction parallel to the substrate.
[0018] FIGS. 4A-4B are views showing an apparatus for producing the
magnetic recording medium having a nanoparticle layer wherein the
easy axis of magnetization of nanoparticles is oriented in the same
direction inclined to the substrate at a 45-degrees.
[0019] FIG. 5A-5B is a view showing an apparatus for producing the
magnetic recording medium having a nanoparticle layer wherein easy
axis of magnetization of nanoparticles is oriented in the same
direction vertical to the substrate.
[0020] FIG. 6 is a side view of the magnetic recording medium
having a nanoparticle layer wherein easy axis of magnetization of
nanoparticles is oriented in the same direction vertical to the
substrate.
[0021] FIGS. 7A-7D are side views showing a manufacturing process
for producing the magnetic recording medium having a nanoparticle
layer wherein the easy axis of magnetization of nanoparticles is
oriented in the same direction vertical to the substrate.
[0022] FIGS. 8A-8C are top and side views showing a manufacturing
process for producing a magnetic recording medium having a
nanoparticle layer by Langmuir-Blodgett method.
[0023] FIG. 9A-9C are side views showing a prior art manufacturing
process for producing a magnetic recording medium having a
nanoparticle layer by spin coating method.
[0024] FIG. 10A-10B are a side view and a perspective view showing
a magnetic read/write processes by using a head system comprising
separate read and write heads.
[0025] FIG. 11A-11B are a side view and a perspective view showing
a optically assisted magnetic read/write processes by using a head
system comprising separate read and write heads.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] In the magnetic recording medium as described above, the
nanoparticles may contain at least one magnetic metal element
selected from Fe, Co, Ni, Mn, Sm, Pt, Pd, and the like. The
nanoparticles may also be magnetic nanoparticles comprising an
intermetallic compound of the aforesaid elements, a binary alloy of
said elements, or a ternary alloy of said elements. In view of the
expected higher recording density in near future, the preferred are
magnetic nanoparticles having the composition of FePt or FePd
having a large uniaxial anisotropy constant (Ku), or a ternary
alloy comprising FePt or FePd and a third element. The third
element used may be Cu, Ag, Au, Ru, Rh, Ir, Pb, or Bi, as well as
other elements. Magnetic nanoparticles having a structure
comprising the core of a binary alloy which is typically FePt or
FePd and the surrounding shell comprising the aforementioned
ternary element, Pt or Pd are also useful.
[0027] The organic compound which is present between the array of
nanoparticles may be the organic compound coating the
nanoparticles. Such organic compound may be an unsaturated fatty
acid compound such as oleic acid, or an amine compound of an
unsaturated fatty acid such as oleylamine. The compounds which may
be used also include a compound having thiol group, as well as a
compound having at least one carbon-carbon double bond or triple
bond. Other organic compounds may also be used for such
coating.
[0028] The organic compound between the array of nanoparticles may
further contain a compound which is capable of binding the organic
compound coating the nanoparticles when it is irradiated with a
light beam or a radiation or by applying heat. To be more specific,
the compound represented by the following general formulae (1) to
(4) may be used. ##STR1##
[0029] In the formulae, R1 to R9 are independently a functional
group selected from carboxylic acids, phosphonic acids, phosphinic
acids, sulfonic acids, sulfinic acids, thiols, hydroxyls, and
hydrogen atom; or a hydrocarbon group containing carbon-carbon
double bond or ether bond. The compound represented by the general
formulae (1) to (4) are crosslinking agents, and crosslinking
agents having other structures may also be used.
[0030] The recording layer of the magnetic recording medium
according to the present invention may be constituted from a
monolayer film or a multilayer film of nanoparticles. The monolayer
or the multilayer nanoparticle layer may be formed by using
Langmuir-Blodgett (LB) method as shown in FIG. 8A-8C. When LB
method is used, the nanoparticle layer may be formed by the
procedure as described below. First, a colloid solution of the
nanoparticles which have been coated with an organic compound 2 is
gradually added dropwise onto the surface of clean water 22 that
has been filled in a trough 21 to form a monolayer film of
nanoparticles wherein the nanoparticles are sparsely arranged.
Next, after evaporating the solvent, the nanoparticle monolayer
film of sparsely arranged nanoparticles is gently compressed by a
moving barrier 23 to the direction 24, and when the compression is
terminated at the pressure wherein the distance between the
nanoparticle is at its least while maintaining the form of the
monolayer film, the film wherein the nanoparticles are packed at
their closest is obtained. Then, the substrate or the substrate
having an underlying layer or a soft magnetic layer formed thereon
held at horizontal position is brought in contact with the water
surface, and pulled up to thereby transfer the monolayer film onto
the substrate and obtain the Langmuir-Blodgett (LB) film comprising
the monolayer film of nanoparticles. A LB multilayer film
comprising a laminate of nanoparticle monolayer films may also be
produced by repeating the procedures as described above.
[0031] The recording layer comprising the nanoparticle layer may
also be formed by spin coating as shown in FIG. 9A-9C wherein the
colloid solution 25 of the nanoparticles is dropped onto the
surface of the substrate and a thin film is formed by rotating the
substrate to the direction 26. When the molecular weight and the
molecular structure of the compound coating the nanoparticles is
adequately selected, and the concentration of the colloid solution
is adjusted, and the rotation conditions are optimized, production
of a recording layer comprising a substantially ordered array of
closely packed nanoparticles is enabled. Methods other than those
described above may also be employed for producing the recording
layer comprising the nanoparticle layer.
[0032] The nanoparticles in the thus formed nanoparticle layer have
cubic crystal fcc structure, and the nanoparticles are scarcely
magnetized. Therefore, crystallographic structure of the
nanoparticles needs to be converted to L10 ordered structure for
magnetization. Referring to FIGS. 7A-7D, when the nanoparticle
layer is irradiated with an infrared beam 9, the infrared beam is
absorbed by the nanoparticles comprising a metal element 1 and
turns into heat which causes partial change in crystallographic
structure of the nanoparticles. The infrared beam 9 is well
absorbed by the nanoparticles comprising a metal element 1 while it
is less likely to be absorbed by the organic compound 2 or the
crosslinking agent coating the nanoparticles, and therefore, the
crystallographic structure of the nanoparticles can be converted
from the cubic crystal fcc to L10 ordered structure for
magnetization 20 of the nanoparticles without changing the quality
of the organic compound 2 between the nanoparticles by adjusting
the intensity and irradiation time of the infrared beam. Degree of
the conversion of the nanoparticles from the cubic crystal fcc to
the L10 ordered structure can be controlled by means of the
infrared beam irradiated in this procedure. Conversion to the
ordered structure can proceed to the level of 100% for further
magnetization and ferromagnetism by increasing the intensity or the
irradiation time of the infrared beam. The infrared beam used may
preferably have a long wavelength of 600 nm or longer, and an
infrared laser beam may be used for the infrared beam.
[0033] After the magnetization as described above, as shown in FIG.
7C, a magnetic field 16 is applied to orient the easy axis of
magnetization of the each nanoparticle to a direction substantially
parallel to a direction at a particular angle with the substrate
surface. In this process, the direction of the magnetic field may
be set parallel to the substrate surface, at 45 degrees to the
substrate surface, perpendicular to the substrate surface, or at
another selected angle. The magnetic field used may be either a
static magnetic field wherein the direction and the intensity of
the magnetic field does not change with time, or a pulse magnetic
field wherein the direction of the magnetic field is constant while
the intensity of the magnetic field alters with time. When the
magnetic field is applied to the nanoparticle layer which has been
magnetized as described above, the easy axis of magnetization of
the each nanoparticle can be oriented to a direction substantially
parallel to a direction at a particular angle with the substrate
surface.
[0034] Next, as shown in FIG. 7D, the nanoparticle layer is
irradiated with an ultraviolet beam 13 to fix the direction of the
easy axis of magnetization. The ultraviolet beam irradiated is
absorbed by the organic compound 2 between the nanoparticles to
induce photochemical or thermochemical reaction to crosslink or
bind the organic compound. When an organic compound such as a
crosslinking agent capable of binding the organic compound coating
the nanoparticles is present between the nanoparticles,
crosslinking efficiency will be improved. The ultraviolet beam
irradiated is preferably a short wavelength beam having a
wavelength of up to 400 nm. The crosslinking efficiency can be
further improved by adequately adjusting the structure of the
crosslinking agent for crosslinking the organic compound between
the nanoparticles, and also, by adjusting the wavelength, the
intensity, and the irradiation time of the ultraviolet beam.
[0035] When the magnetization by the irradiation of the infrared
beam is insufficient, the nanoparticles may be further ordered by
conducting a heat treatment at a temperature of up to 300.degree.
C. for an arbitrary period after the step of binding the organic
compound by the ultraviolet irradiation.
[0036] When a nanoparticle layer is irradiated with an infrared
beam for magnetization, a magnetic field is then applied at a
particular angle with the substrate surface to orient the easy axis
of magnetization of the nanoparticles in the direction of the
magnetic field, and the nanoparticle layer is further irradiated
with an ultraviolet beam to crosslink the organic compound between
the nanoparticle to thereby fix the nanoparticles as described
above, a nanoparticle layer wherein the easy axis of magnetization
is substantially parallel to a direction at a particular angle to
the substrate surface can be obtained. In this procedure, when a
magnetic field perpendicular to the substrate surface is applied,
while adequately adjusting the intensity and the time of the
magnetic field application, the layer obtained will be a
perpendicular magnetic layer wherein number of nanoparticles
wherein angle between the direction perpendicular to the substrate
surface and the easy axis of magnetization of the nanoparticles is
up to 5 degrees is at least 90% of the total number of
nanoparticles included in the nanoparticle layer. Such magnetic
layer exhibits favorable perpendicular magnetic anisotropy as well
as excellent magnetic properties.
[0037] The recording of the information on the nanoparticle medium
having the nanoparticle layer exhibiting the favorable
perpendicular magnetic anisotropy as described above may be
accomplished by a perpendicular magnetic recording system wherein
the main component of the leakage magnetic field from the write
head is perpendicular to the in-plane direction of the substrate.
The recording may be also accomplished by a thermomagnetic or a
magneto-optical recording system wherein magnetic recording is
conducted while the recording area of the medium is selectively
irradiated with heat or light.
[0038] The apparatus used for producing a magnetic recording medium
wherein easy axis of magnetization of the nanoparticles is oriented
at a direction which is at a particular angle to the substrate
surface may be the apparatus as shown in FIG. 3. This apparatus has
a rotating section 8 which rotates the substrate 3 (see rotation
direction 17 indicated) bearing the nanoparticle layer 5 at an
arbitrary rotation speed around a particular rotation axis 7, and
in this apparatus, an infrared irradiating section 10 for
irradiating an infrared beam 9 to a particular region of said
substrate, a magnetic field applying section 12 having coils 11 for
applying a magnetic field to said particular region after the
infrared irradiation (see magnetic field direction 16), and an
ultraviolet irradiating section 14 for irradiating a ultraviolet
beam 13 to said particular region after the magnetic field
application are concentrically arranged around on a circle 15 whose
center is the rotation center. After such procedure, the organic
compound coating the nanoparticle 1 or the compound 6 derived from
the organic compound coating the nanoparticle will be present
between the nanoparticles.
EXAMPLES
[0039] Next, the present invention is described in further detail
by referring to the following Examples which by no means limit the
scope of the invention.
Example 1
[0040] Referring to FIGS. 5A & 5B, Spherical magnetic
nanoparticles having a particle dispersion standard deviation
degree of up to 10% and a diameter in the range of 1 to 20 nm were
chemically synthesized, and the nanoparticles were classified by
size in a centrifuge such that each class had a diameter dispersion
standard deviation of up to 5%. In the thus produced colloid
solution of the nanoparticles, nanoparticles comprising a magnetic
metal element surrounded by a coating of an organic compound were
dispersed as colloid. Next, the colloid solution of the
nanoparticles as described above was dropped onto a soft magnetic
layer which had been deposited on a glass substrate by sputtering,
and the substrate was rotated for spin coating of the colloid
solution to obtain a monolayer film of the nanoparticles which was
then subjected to a prebaking at 80.degree. C. for 5 minutes. The
substrate having the thus formed nanoparticle layer thereon was
rotated such that an arbitrary region of the nanoparticle layer was
irradiated with an infrared beam 9 having a wavelength of 800 nm,
and a magnetic field 16 in the direction perpendicular to the
substrate surface was applied to this region at the very moment
when this region passed between a pair of coils 11 having magnetic
poles arranged on opposite sides of the substrate, and this region
was further irradiated with an ultraviolet beam 13 having a
wavelength of 200 nm immediately after passing between the coils. A
perpendicular magnetic recording medium having a nanoparticle layer
wherein the easy axis of magnetization 18 as shown in FIG. 6 is
oriented at a direction 19 perpendicular to the in-plane direction
of the substrate is thereby produced. This is the best mode.
Example 2
[0041] A monolayer film of the nanoparticle was formed by
Langmuir-Blodgett method as shown in FIG. 8A-8C instead of the spin
coating used in Example 1. The substrate having the thus formed
nanoparticle layer thereon was rotated such that an arbitrary
region of the nanoparticle layer was irradiated with an infrared
beam having a wavelength of 800 nm, and a magnetic field in the
direction perpendicular to the substrate surface was applied to
this region at the very moment when this region passed between a
pair of coils having magnetic poles arranged on opposite sides of
the substrate, and this region was further irradiated with an
ultraviolet beam having a wavelength of 200 nm immediately after
passing between the coils. A perpendicular magnetic recording
medium having a nanoparticle layer wherein the easy axis of
magnetization had been oriented at a direction perpendicular to the
in-plane direction of the substrate was thereby produced.
Example 3
[0042] To the colloid solution of nanoparticles used in Example 1
was added a crosslinking agent represented by the general formula
(1): ##STR2## at an amount of 20% by weight of the colloid. The
colloid solution having the crosslinking agent added thereto was
dropped onto the surface of clean water to form a LB monolayer film
of nanoparticles by Langmuir-Blodgett method. This LB monolayer
film was transferred onto the substrate. When this LB monolayer
film was observed under SEM, the resulting array of nanoparticles
substantially had closest packed structure.
[0043] The substrate having the thus formed nanoparticle layer
thereon was rotated such that an arbitrary region of the
nanoparticle layer was irradiated with an infrared beam having a
wavelength of 800 nm, and a magnetic field in the direction
perpendicular to the substrate surface was applied to this region
at the very moment when this region passed between a pair of coils
having magnetic poles arranged on opposite sides of the substrate,
and this region was further irradiated with an ultraviolet beam
having a wavelength of 200 nm immediately after passing between the
coils. A perpendicular magnetic recording medium having a
nanoparticle layer wherein the easy axis of magnetization had been
oriented at a direction perpendicular to the in-plane direction of
the substrate was thereby produced.
Example 4
[0044] Referring to FIGS. 4A and 4B, the procedure of Example 3 was
repeated by using a colloid solution of nanoparticles having a
crosslinking agent added thereto to form a nanoparticle monolayer
film by the LB method. The substrate having the thus formed
nanoparticle layer thereon was rotated such that an arbitrary
region of the nanoparticle layer was irradiated with an infrared
beam having a wavelength of 800 nm and a magnetic field at an angle
of 45 degrees to the substrate surface was applied to this region
at the very moment when the region passed between a pair of coils
having a pair of magnetic poles arranged on opposite sides of the
substrate at an angle of 45 degrees with the substrate, and this
region was irradiated with an ultraviolet beam having a wavelength
of 200 nm immediately after passing between the coils. A magnetic
recording medium having a nanoparticle layer wherein the easy axis
of magnetization had been oriented at 45 degrees to the in-plane
direction of the substrate was thereby produced.
Example 5
[0045] Referring to FIGS. 5A and 5B, the magnetic nanoparticle
medium produced in Example 3 was evaluated by using a sample
vibration magnetometer. A magnetization curve exhibiting excellent
magnetic properties including a perpendicular coercive force of 800
kA/m (10000 Oe), a coersive force squareness ratio S* of 0.8, and a
residual magnetization of 200 emu/cc was obtained.
Example 6
[0046] Referring to FIG. 10A-10B, the magnetic nanoparticle medium
27 produced in Example 3 was combined with a head system 36
comprising separate read and write heads employing a thin film
single pole head for perpendicular magnetic recording for the write
head 35 composed of an auxiliary pole 32, a main pole 33, and coils
34, and a GMR element 30 between shields 28, 29 for the read head
31 to evaluate the output. A magnetic flux 38 orients the direction
of magnetization 20 of the medium to the same direction to the
magnetic field while the medium moves to the direction 37. At the
output evaluation, a magnetic nanoparticle medium 27 is rotated to
the direction 40, and the head system 36 is mounted on an arm 39. A
peak-to-peak output of about 1 mV was measured at a recording
density of 100 kfci. The medium also exhibited an abrasion
resistance equivalent to a conventional medium wherein the
recording layer had been formed by sputtering.
Example 7
[0047] Referring to FIG. 11A to 11B, a read/write experiment was
conducted by using an optically assisted magnetic recording head 43
wherein only the recording area is heated by a light beam 42 from a
laser 41 for the writing, and a GMR element 30 for the read head
instead of the perpendicular magnetic recording used in Example 6.
A peak-to-peak output of about 1 mV was measured at a recording
density of 100 kfci.
Example 8
[0048] The magnetic nanoparticle medium produced in Example 3 was
observed under SEM. No disturbance in the particle array or
agglomeration of the particles induced by the heat treatment were
observed. Observation under AFM revealed that the medium had a
surface roughness Ra of up to 0.8.
[0049] In Example 3 as described above, the crosslinking agent used
was the one represented by the general formula (1). The
crosslinking agent of the formula (1), however, could be replaced
with a compound represented by any one of the general formulae (2),
(3), and (4). It is of course possible to conduct the following
Examples 4 to 8 by using the product prepared by using the compound
represented by any one of the general formulae (2), (3), and (4).
##STR3##
[0050] In the formulae, R1 to R9 are independently a functional
group selected from carboxylic acids, phosphonic acids, phosphinic
acids, sulfonic acids, sulfinic acids, thiols, hydroxyls, and
hydrogen atom; or a hydrocarbon group containing carbon-carbon
double bond or ether bond. R1 to R9 may be the same or
different.
[0051] As described above, a magnetic recording medium provided
with a magnetic recording layer wherein nanoparticles are arranged
on the substrate in an ordered array and an organic compound is
present between the nanoparticles could be produced, and in this
medium, no high temperature heat treatment was necessary, flatness
of the nanoparticle layer was improved compared to the conventional
medium comprising the magnetic nanoparticles, the underlying layer
or the soft magnetic layer did not experience deterioration, easy
axis of magnetization of the nanoparticles was substantially
parallel to a direction at a particular angle to said substrate
surface, and magnetic properties were excellent. This medium could
be recorded with information by magnetic recording.
Example 9
[0052] Referring to FIGS. 3A and 3B, the procedure of Example 3 was
repeated by using a colloid solution of nanoparticles having a
crosslinking agent added thereto to form a nanoparticle monolayer
film by the LB method. The substrate having the thus formed
nanoparticle layer thereon was rotated such that an arbitrary
region of the nanoparticle layer was irradiated with an infrared
beam having a wavelength of 800 nm and a magnetic field in the
direction parallel to the substrate surface was applied to this
region at the very moment when the region passed the area in which
a pair of coils having a pair of magnetic poles arranged on the
same side of the substrate in the direction parallel to the
substrate, and this region was irradiated with an ultraviolet beam
having a wavelength of 200 nm immediately after passing between the
coils. A magnetic recording medium having a nanoparticle layer
wherein the easy axis of magnetization had been oriented in the
direction parallel to the substrate was thereby produced.
[0053] Although the above examples are provided applicants also
envision variations and equivalents to the disclosure discussed
above to be within the scope of this disclosure and the claims.
* * * * *