U.S. patent application number 11/057220 was filed with the patent office on 2005-06-23 for magnetic recording medium, magnetic recording apparatus using the same, and method and apparatus for manufacturing the magnetic recording medium.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Nakamura, Atsushi, Suzuki, Yoshio, Tanahashi, Kiwamu, Tsuchiya, Yuko.
Application Number | 20050134988 11/057220 |
Document ID | / |
Family ID | 32396295 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050134988 |
Kind Code |
A1 |
Nakamura, Atsushi ; et
al. |
June 23, 2005 |
Magnetic recording medium, magnetic recording apparatus using the
same, and method and apparatus for manufacturing the magnetic
recording medium
Abstract
A magnetic recording apparatus provides improved resolution and
S/N without adversely affecting thermal stability. An angle formed
by the direction of easy magnetization of a recording layer and the
direction normal to a magnetic recording medium is in the range
between 5.degree. and 55.degree., the easy magnetization direction
is from a back surface of the recording layer toward a front
surface thereof, and when a recording track direction is from the
upstream of the direction of transportation of the medium toward
the downstream thereof, an angle formed by the direction of a
projection of the easy magnetization direction on the medium plane
and the recording track direction is in the range between 0.degree.
and 70.degree..
Inventors: |
Nakamura, Atsushi; (Kodaira,
JP) ; Suzuki, Yoshio; (Tokyo, JP) ; Tanahashi,
Kiwamu; (Kokubunji, JP) ; Tsuchiya, Yuko;
(Tokorozawa, JP) |
Correspondence
Address: |
REED SMITH LLP
Suite 1400
3110 Fairview Park Drive
Falls Church
VA
22042
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
32396295 |
Appl. No.: |
11/057220 |
Filed: |
February 15, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11057220 |
Feb 15, 2005 |
|
|
|
10601979 |
Jun 24, 2003 |
|
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Current U.S.
Class: |
360/55 ;
G9B/5.044; G9B/5.156; G9B/5.236 |
Current CPC
Class: |
G11B 5/11 20130101; G11B
5/09 20130101; G11B 5/74 20130101; G11B 5/64 20130101; G11B
2005/0002 20130101; Y10T 428/11 20150115; G11B 5/488 20130101; G11B
2005/0005 20130101; G11B 5/02 20130101; G11B 5/012 20130101; G11B
5/82 20130101; G11B 5/4886 20130101; G11B 5/1278 20130101; G11B
2005/0029 20130101 |
Class at
Publication: |
360/055 |
International
Class: |
G11B 005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2003 |
JP |
2003-86318 |
Nov 28, 2002 |
JP |
2002-346124 |
Claims
What is claimed is:
1. A method of manufacturing a magnetic recording medium, the
method comprising the steps of: forming a nanoparticle layer by
disposing nanoparticles on a substrate, the nanoparticles
comprising alloy particles containing at least one element selected
from the group consisting of Fe, Co, Ni, Mn, Sm, Pt, and Pd,
wherein the alloy particles are coated with an organic compound;
irradiating the nanoparticle layer with infrared light to produce
magnetic nanoparticles; applying a magnetic field to the
nanoparticle layer to control the magnetization direction of the
magnetic nanoparticles in substantially one direction; and
irradiating the nanoparticle layer with ultraviolet light to
cross-link the organic compound, wherein the angle formed by the
direction of the magnetic field applied in the magnetic field
applying step and the direction normal to the substrate is not less
than 5.degree. and not more than 60.degree..
2. A magnetic recording medium manufacturing apparatus comprising:
means for irradiating a nanoparticle layer disposed on a substrate
with infrared light to produce magnetic nanoparticles, the
nanoparticles comprising alloy particles containing at least one
element selected from the group consisting of Fe, Co, Ni, Mn, Sm,
PT AND Pd, wherein the alloy particles are coated with an organic
compound; means for applying a parallel magnetic field to the
nanoparticle layer, the magnetic field forming an angle of not less
than 5.degree. and not more than 60.degree. with the direction
normal to the substrate in order to control the direction of
magnetization of the magnetic particles in substantially one
direction; means for applying ultraviolet light to the nanoparticle
layer to cross-link the organic compound; and means for shifting
the position of irradiation of the infrared light and ultraviolet
light on the substrate.
3. A magnetic recording apparatus comprising: a magnetic recording
medium; a single pole type (SPT) head; a slider on which the SPT
head is mounted; a suspension arm for securely fastening the
slider; and an actuator for supporting the suspension arm; wherein
the magnetic recording medium comprises at least a soft magnetic
underlayer and a recording layer, and wherein the angle formed by
the easy magnetization direction of the recording layer and the
direction normal to the medium is not less than 15.degree. and not
more than 55.degree..
4. The magnetic recording apparatus according to claim 3, wherein
the SPT head can be transported to an arbitrary position on the
recording medium by the movement of the actuator where it can
record information.
5. The magnetic recording apparatus according to claim 3, wherein
the SPT head comprises at least: a main pole, an auxiliary pole and
a shield disposed downstream of the direction of transportation of
the medium with respect to the main pole and having a wider width
than the main pole.
6. A magnetic recording apparatus comprising: a magnetic recording
medium; a single pole type (SPT) head; a slider on which the SPT
head is mounted; a suspension arm for securely fastening the
slider; and an actuator for supporting the suspension arm, wherein
the magnetic recording medium comprises at least a soft magnetic
underlayer and a recording layer, wherein when the easy
magnetization direction of the recording layer is from a back
surface of the recording layer toward a front surface thereof and
when the direction of recording tracks is from the upstream of the
direction of transportation of the medium toward the downstream
thereof, the direction of a projection of the easy magnetization
direction on the medium plane substantially coincides with the
recording track direction.
7. The magnetic recording apparatus according to claim 6, wherein
the angle formed by the easy magnetization direction of the
recording layer and the direction normal to the medium is not less
15.degree. and not more than 55.degree..
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a magnetic recording medium
characterized by its direction of easy magnetization, a magnetic
recording apparatus on which the recording medium is mounted, and a
method and apparatus for manufacturing the magnetic recording
medium.
[0003] 2. Background Art
[0004] In order to obtain increased areal density in magnetic
recording apparatus, a perpendicular magnetic recording technique
has been proposed to replace the conventional longitudinal magnetic
recording technique. In perpendicular magnetic recording, the
direction of recorded magnetization created in a recording medium
is perpendicular to a film plane. This technique has the advantage
that the fine recorded magnetization is thermally stable. As the
magnetic head for perpendicular magnetic recording, a dual element
write-read head can be considered. The read head employs a
magnetoresistive head that is conventionally used in longitudinal
magnetic recording. The write head can employ a single pole type
("SPT") head comprised of a main pole and an auxiliary pole. By
employing a double-layer perpendicular recording medium comprising
a recording layer and an underlayer of soft magnetic material
formed on the back surface of the recording layer, the SPT head can
advantageously produce a stronger magnetic field than a ring-type
head that is conventionally used in longitudinal magnetic
recording. While there is a need to improve the perpendicular
magnetic recording properties such as, for example, resolution and
S/N, if the average grain size of the recording layer is reduced to
improve S/N, or if the thickness of the recording layer is reduced
to obtain a steeper head field gradient and thereby improve
resolution, the thermal stability of the recording medium is
adversely affected.
[0005] Another example of magnetic recording is oblique magnetic
recording that is widely used in magnetic tape media. This is a
technique in which the direction of recorded magnetization is
inclined with respect to the direction normal to the film plane,
and in which a ring head is used for recording. It can achieve a
high S/N recording. In the case of magnetic tape media, it is well
known that different recording characteristics are obtained when
the direction in which recorded magnetization is inclined is
reversed with respect to the direction of recording tracks.
Specifically, when the direction of recorded magnetization is from
the back surface of the tape medium toward the front surface
thereof and the direction of recording tracks is from the upstream
of the direction of transportation of the tape medium to the
downstream thereof, better recording characteristics are obtained
when the direction of recorded magnetization as projected on the
tape medium plane is opposite that of the recording tracks. This is
described in IEEE Transactions on Magnetics, MAG-19 (1983), pp.
1635-1637, for example. An attempt to apply this oblique recording
technique to disc media is disclosed in JP Patent Publication
(Kokai) No. 58-128023 A (1983). This publication teaches that when
a ring head is used for recording, an improved reproduced output
can be obtained when a projection of the longitudinal axis of the
needle-like particles forming a magnetic recording medium on the
substrate surface is substantially parallel to the circumference of
the disc while, at the same time, the longitudinal axis is inclined
with respect to a line normal to the substrate surface by
45.degree. or more. Further, JP Patent Publication (Kokai) No.
9-212855 A (1997) describes the effect of inclining the axis of
easy magnetization when a medium having an underlayer is recorded
using an SPT head. According to this publication, an improved S/N
can be obtained when a projection of the axis of easy magnetization
on the magnetic recording medium is inclined by 90.degree. with
respect to the direction of tracks. None of these prior art
documents, however, analyze the effect of the relationship between
the transport direction of the magnetic recording medium and the
direction of inclination of the axis of easy magnetization.
[0006] A conventional method of manufacturing magnetic recording
media, such as longitudinal or perpendicular magnetic recording
media, involves the deposition of a thin film of a magnetic
material for forming a magnetic recording medium on a substrate by
physical vapor deposition, such as vacuum deposition or sputtering.
In a longitudinal magnetic recording medium, a recording layer is
formed by epitaxial growth on the surface of an underlayer whose
crystal orientation is controlled, and the crystals are oriented
such that the axis of easy magnetization is parallel to the film
surface. In the film plane, the individual crystal particles either
have generally random axes of easy magnetization, or are provided
with a weak anisotropy so that the magnetization is predisposed to
be directed toward the circumference of the disc-shaped magnetic
recording medium. The latter is realized by employing a substrate
on the surface of which fine grooves called texture are
mechanically formed. However, in order to improve recording
density, the spacing between the magnetic head and the magnetic
recording medium must be reduced. For example, JP Patent
Publication (Kokai) Nos. 2001-14664 A and 2002-109729 A disclose
techniques of providing circumferential anisotropy by employing a
smooth substrate without texture and controlling the direction of
the traveling particles during the formation of the thin film such
that it is inclined away from a line normal to the substrate and
toward the circumference.
[0007] A totally different manufacturing method is disclosed in JP
Patent Publication (Kokai) No. 2000-48340 A, whereby magnetic
nanoparticles are arranged in an ordered manner. This publication,
however, does not describe the method of controlling the magnetic
anisotropy of particles.
[0008] As mentioned above, the head for perpendicular magnetic
recording comprises an SPT head comprised of a main pole and an
auxiliary pole is used. A head structure has been proposed for
improving the field gradient of the SPT head, in which a shield
made of soft magnetic thin film is disposed near the main pole.
Examples are disclosed in U.S. Pat. No. 4,656,546 and IEEE
Transactions on Magnetics, Vol. 38 (2002), pp. 163-168, pp.
1719-1724, and pp. 2216-2218. The heads described in these
publications are for perpendicular magnetic recording and are not
for media with an inclined axis of easy magnetization. These prior
art publications mention that the head of this type can provide a
steeper field gradient than the conventional SPT head. However,
they either make little mention about the reduction of magnetic
field strength, or state that the reversal of magnetization of the
perpendicular magnetic recording medium would be easier due to the
increase in the in-plane components of magnetic field, or that the
magnetic field strength could be ensured by making the main pole
thicker and reducing the head-media spacing.
[0009] In the prior art, there has not been proposed a method of
improving resolution and S/N without adversely affecting the
thermal stability in the perpendicular magnetic recording technique
in which a medium having an underlayer is recorded using an SPT
head. Further, in the art of recording a medium having an
underlayer in which the axis of easy magnetization is inclined with
respect to a line normal to the medium, there has been no analysis
of the case when the transportation direction of the medium is
nearly parallel to the direction of a projection of the direction
of easy magnetization on the medium plane.
[0010] Furthermore, in the above-mentioned prior art, when a
perpendicular magnetic recording medium having an underlayer is
recorded using an SPT head with the structure in which a shield
made of soft magnetic thin-film is disposed near the main pole,
sufficient magnetic strength cannot be obtained. If a material with
a large magnetic anisotropy is employed for the recording medium in
order to allow magnetic recording to be carried out at high areal
density without damaging the thermal stability, satisfactory
recording cannot be carried out in the perpendicular recording
technique.
SUMMARY OF THE INVENTION
[0011] It is therefore an object of the invention to provide a
magnetic recording medium with high resolution and S/N that has
thermal stability comparable to that of the conventional
perpendicular magnetic recording media. Another object of the
invention is to provide a magnetic recording apparatus for
achieving higher areal density using the magnetic recording medium
than the conventional perpendicular magnetic recording apparatus.
It is yet another object of the invention to provide a method and
apparatus for manufacturing the magnetic recording medium.
[0012] To achieve the objects, the invention provides a magnetic
recording medium comprising at least a soft magnetic underlayer and
a recording layer. The direction of easy magnetization of the
recording layer is inclined from the direction normal to the
medium. When the easy magnetization direction is from the back
surface of the recording layer to the upper surface thereof, and
the direction of recording tracks is from the upstream of the
direction of transportation of the medium toward the downstream
thereof, the direction of the projection of the easy magnetization
direction on the medium plane substantially coincides with the
recording track direction. This is opposite the direction that is
suitable in the case of the combination of a tape medium and a ring
head, as described above. The angle formed by the direction of the
projection of the easy magnetization direction on the medium plane
and the recording track direction may be not more than 70.degree..
The easy magnetization direction is characteristically inclined
from the normal direction of the medium by an angle of not less
than 5.degree. and not more than 55.degree..
[0013] The magnetic recording apparatus according to the invention
records information on this medium using an SPT head. The apparatus
comprises at least an SPT head, a slider on which the SPT head is
mounted, a suspension arm for securely fastening the slider, and an
actuator for supporting the suspension arm. The SPT head can be
transported to an arbitrary position on the disc-shaped rotating
recording medium by the movement of the actuator where it can
record information. The SPT head includes at least a main pole and
an auxiliary pole. It may further include a shield disposed mainly
downstream of the direction of transportation of the medium
relative to the main pole, the shield having a wider width than the
main pole. When an SPT head with a shield is used, the angle formed
by the easy magnetization direction of the recording layer and the
direction normal to the medium should preferably be not less than
15.degree. and not more than 55.degree..
[0014] The magnetic recording medium of the invention can be
manufactured by roughly two kinds of methods. One is similar to the
conventional method of manufacturing longitudinal or perpendicular
magnetic recording media, whereby a thin film of a magnetic
material forming the medium is deposited on a substrate by physical
vapor deposition such as vacuum deposition or sputtering. The
magnetic recording medium of the invention can be manufactured by
allowing deposition or sputtering particles to be incident in a
direction inclined from the direction normal to the substrate.
Specifically, a mask plate, for example, may be placed between a
target and the substrate that passes only those particles flying
from the target toward the substrate by the conventional sputtering
technique that are inclined by a certain angle from the direction
normal to the substrate. In this case, a uniform film can be
obtained on the entire substrate surface by rotating the substrate
and the target during film formation. The inventive magnetic
recording medium can also be manufactured without using the mask
plate or a slit by a sputtering method such as ion beam sputtering
that provides directional sputtering particles, while rotating the
substrate.
[0015] Another conceivable method involves the use of a thin film
of an intermetallic compound in the recording layer that has an
L1.sub.0-type crystal structure, in which a disordered alloy is
ordered by thermal treatment to exhibit ferromagnetism. According
to this method, a nanoparticle layer comprised of fine disordered
alloy particles of the order of nanometers and an organic compound
is formed on a substrate. The particles are irradiated with
infrared laser to heat and order them. When the particles start
getting ordered, a magnetic field is simultaneously applied
externally in a direction inclined from the direction normal to the
film plane, thereby causing the easy magnetization direction of the
particles to be oriented in the magnetic field direction.
Thereafter, ultraviolet light is irradiated so that the organic
compound is cross-linked and the nanoparticles are fixed.
[0016] In this case, the average particle size is not more than 20
nm and the alloy comprises at least one element selected from the
group consisting of Fe, Co, Ni, Mn, Sm, Pt, and Pd. The angle
formed by the direction of the applied magnetic field and the
direction normal to the substrate during the step of applying a
magnetic field is not less than 5.degree. and not more than
60.degree.. Examples of the organic compound include oleic acid,
carboxylic acid, phosphonic acid, phosphinic acid, sulfonic acid,
sulfinic acid, and thiol.
[0017] The magnetic recording medium manufacturing apparatus
according to the invention for manufacturing such a medium
comprises means for irradiating the nanoparticle layer on the
substrate in which the nanoparticles are orderly arranged with
infrared light to render the nanoparticles into magnetic
nanoparticles. It also comprises means for applying a parallel
magnetic field to the nanoparticle layer, the magnetic field
forming an angle of not less than 5.degree. and not more than
60.degree. with the direction normal to the substrate, thereby
controlling the direction of the magnetization of the magnetic
nanoparticles in substantially one direction. The apparatus further
comprises means for irradiating the nanoparticle layer with
ultraviolet light to cross-link the organic compound, and means for
shifting the position of irradiation of infrared light and
ultraviolet light on the substrate.
[0018] The magnetic recording medium and the magnetic recording
apparatus according to the invention are not limited to magnetic
disc apparatus for recording a rotating, disc-shaped substrate. The
invention can be applied to any recording apparatus in which the
position of the head relative to the medium is moved, including a
magnetic tape apparatus.
[0019] By utilizing the magnetic recording medium according to the
invention, improved resolution and S/N can be obtained without
adversely affecting the thermal stability. Further, by mounting the
magnetic recording medium according to the invention, a magnetic
recording apparatus with an improved areal density can be
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows a cross-sectional view of a magnetic recording
medium according to an embodiment of the invention.
[0021] FIG. 2 schematically shows a magnetic disc apparatus
according to an embodiment of the invention.
[0022] FIG. 3 schematically illustrates the arrangement of the head
and the medium in the magnetic recording process in an embodiment
of the invention.
[0023] FIG. 4 schematically shows the easy magnetization direction
and the medium transportation direction of the magnetic recording
medium according to an embodiment of the invention.
[0024] FIG. 5 is a chart showing the variation of resolution
relative to the easy magnetization direction in an embodiment of
the invention.
[0025] FIG. 6 is a chart showing the variation of S/N relative to
the easy magnetization direction in an embodiment of the
invention.
[0026] FIG. 7 is a chart showing the variation of the required
recording magnetic field relative to the easy magnetization
direction in an embodiment of the invention.
[0027] FIG. 8 shows the easy magnetization direction of a medium
and the medium transportation direction in an embodiment of the
invention.
[0028] FIG. 9 is a chart showing the variation of resolution
relative to the easy magnetization direction in an embodiment of
the invention.
[0029] FIG. 10 is a chart showing the variation of S/N relative to
the easy magnetization direction in an embodiment of the
invention.
[0030] FIG. 11 schematically shows the arrangement of a target, a
mask plate, and a substrate in an embodiment of the invention.
[0031] FIG. 12 schematically shows the arrangement of the direction
of application of a magnetic field and the magnetic recording
medium in an embodiment of the invention.
[0032] FIG. 13 schematically shows a write-read head.
[0033] FIG. 14 schematically shows the arrangement of the poles of
the head as seen from the air bearing surface.
[0034] FIG. 15 is a chart showing the variation of resolution
relative to angle .alpha..
[0035] FIG. 16 is a chart showing the variation of S/N relative to
angle .alpha..
[0036] FIG. 17 schematically shows the shape of a main pole and a
shield as seen from the air bearing surface.
[0037] FIG. 18 schematically shows the shape of a main pole and a
shield as seen from the air bearing surface.
[0038] FIG. 19 shows a modification of the write-read head in which
the position of an auxiliary pole is different.
[0039] FIG. 20 shows another modification of the write-read head in
which the position of an auxiliary pole is different.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0040] The invention will be hereafter described by way of
preferred embodiments with reference made to the drawings.
Embodiment 1
[0041] FIG. 1 schematically shows a cross-section of an example of
the magnetic recording medium according to the invention. A soft
magnetic underlayer 12 is disposed on a substrate 11. A recording
layer 14 is disposed on the soft magnetic underlayer 12 via an
intermediate layer 13. A protective layer 15 is disposed on the
surface of the recording layer 14. The direction of easy
magnetization 16 in the recording layer is inclined away from a
line normal to the medium toward the direction of medium
transportation 17.
[0042] FIG. 2 shows an example of the magnetic recording apparatus
according to the invention. A slider 23 is fixed at the tip of a
suspension arm 22 supported by a rotary actuator 21. At the end of
the slider 23 is mounted a head element 24 that records or
reproduces information on a magnetic recording medium 26 rotating
in a rotation direction 25 as shown. The head element 24 includes
an SPT head as a write head and a magnetoresistive head as a read
head. The head element 24 can be transported and positioned at
different radial positions on the disc by rotating the rotary
actuator 21. Concentric recording tracks 27 are formed on the
medium.
[0043] FIG. 3 shows the arrangement of the head and the medium
during a magnetic recording process in an embodiment of the
invention. The head includes a write head (SPT head) comprised of a
main pole 31, an auxiliary pole 32 and a coil 33. It also includes
a read head having a magnetoresistive film 38 sandwiched between a
pair of shields 32 and 37, one of which is doubled by the auxiliary
pole. The thus constructed head is disposed opposite a magnetic
recording medium including a recording layer 34 and a soft magnetic
underlayer 35. As the coil 33 is energized, a vertical magnetic
field is created between the tip of the main pole 31 and the soft
magnetic underlayer 35, thus recording the recording layer 34 of
the magnetic recording medium. The magnetic flux flowing into the
soft magnetic underlayer 35 is then returned to the auxiliary pole
32, creating a magnetic circuit. Recording takes place while
varying the relative positions of the medium and the head. With the
head fixed and the medium moving, when the recording track
direction is from the upstream of a medium transport direction 36
to the downstream thereof, and when the direction of easy
magnetization is from the back surface of the recording layer
toward the upper surface thereof, the head is disposed such that a
projection of the easy magnetization direction on the medium plane
substantially coincides with the recording track direction.
Because, strictly speaking, the recording tracks are concentric
circles about the center of rotation of the medium, the recording
track direction as used herein refers to the direction of a tangent
to a recording track at a given point.
[0044] FIG. 4 shows a direction 42 of easy magnetization of a
magnetic recording medium 41 used in the present embodiment and the
direction of transportation of the medium. In the embodiment, the
direction 42 of easy magnetization of the magnetic recording medium
41 is inclined from a normal direction 43 of the medium by an angle
.alpha.. When the easy magnetization direction is from the back
surface of the recording layer toward the upper layer thereof, and
a direction 44 of recording tracks is from the upstream of a
direction 45 of transportation of the magnetic recording medium
toward the downstream thereof, a direction 46 of a projection of
the easy magnetization direction 42 on the magnetic recording
medium plane substantially coincides with the recording track
direction 44. The recording track direction 44 is along a line
tangent to a recoding track 47 that is concentric with the
disc-shaped magnetic recording medium 41.
[0045] FIGS. 5 and 6 show the results of computer simulation of
write/read characteristics when the angle .alpha. between the easy
magnetization direction and the normal direction of the magnetic
recording medium was varied. Computation conditions included: an
average particle diameter 12.7 nm of the magnetic particles in the
recording layer; recoding layer film thickness 20 nm; magnetic
anisotropy constant 1.3.times.10.sup.5 J/m.sup.3; saturation
magnetization 0.314 T; underlayer thickness 100 nm; underlayer
saturation flux density 1.8 T; underlayer relative permeability
100; main-pole width 150 nm; main-pole thickness 400 nm; head-media
magnetic spacing 15 nm; and head-medium relative speed 20 m/s. A
low-density recording with a bit length 152 nm and a high-density
recording with a bit length 38 nm were conducted to obtain the
resolution, which is the percentage of high-density output to
low-density output, and the S/N ratio, which is the ratio in dB of
low-density output to high-density noise. The head field strength
was 939 kA/m.
[0046] FIG. 5 shows the resolution for the angle .alpha., while
FIG. 6 shows S/N for the angle .alpha.. The resolution improved
gradually in .alpha..gtoreq.25.degree. against the value at
.alpha.=0.degree.. On the other hand, S/N improved in
5.degree..ltoreq..alpha..ltoreq.55.degree. over .alpha.=0.degree..
Thus, it was revealed that the present invention can provide an
improved S/N when the angle .alpha. between the easy magnetization
direction and the normal direction of the magnetic recording medium
is in the range between 5.degree. and 55.degree.. Particularly,
both the resolution and S/N can be improved in the range of .alpha.
between 25.degree. and 55.degree.. Why the resolution and S/N
improve the greater the value of .alpha. is not clear; presumably,
it has to do with a change in the required recording magnetic
field.
[0047] FIG. 7 plots the required recording magnetic field against
the angle .alpha.. The required recording magnetic field is herein
defined as the head field strength with which an 80% reproduced
output can be obtained with respect to a maximum reproduced output
value determined by varying maximum value of the head field
strength. The bit length was 152 nm. The required recording field
strength monotonously decreased in the range
0.degree..ltoreq..alpha..ltoreq.50.degree.. The maximum recording
field had a constant value in each case when the resolution and S/N
were estimated. Thus, the smaller the required recording field, the
greater was the relative recording field strength during the
estimation of the resolution and S/N, which is believed to be
responsible for the improvements in the resolution and S/N.
[0048] Thus, in accordance with the invention, S/N can be improved
when the angle .alpha. between the easy magnetization direction and
the normal direction of the magnetic recording medium is in the
range 0.degree..ltoreq..alpha..ltoreq.55.degree.. Particularly,
both the resolution and S/N can be improved in the range
25.degree..ltoreq..alpha.- .ltoreq.55.degree.. For example, when
.alpha.=40.degree., the resolution increased by a factor of 1.4 and
S/N improved by 3 dB as compared with when .alpha.=0.degree., that
is when the easy magnetization direction is along the normal
direction of the magnetic recording medium. Further, the thermal
stability of these two media, when expressed as the ratio of
reproduced output after 100 hours to that 10 seconds after
recording, was 0.88 in each case, and thus there was no
difference.
Embodiment 2
[0049] Using the same magnetic recording medium as in Embodiment 1,
when the direction of easy magnetization was from the back surface
of the recording layer toward the front surface thereof, and when
the recording track direction was from the upstream of the
direction of transportation of the magnetic recording medium toward
the downstream thereof, the resolution and S/N were estimated with
varying angles .beta. between the direction of the projection of
the easy magnetization direction on the magnetic recording medium
plane and the recording track direction.
[0050] FIG. 8 shows an easy magnetization direction 82 and a medium
transportation direction 85 of the magnetic recording medium. The
easy magnetization direction 82 is inclined by an angle .alpha.
from a normal direction 83 of the medium. When the easy
magnetization direction 82 was from the back surface of the
recording layer toward the upper surface thereof, and when the
recording track direction 84 was from the upstream of the medium
transportation direction 85 toward the downstream thereof, an angle
.beta. was formed between a direction 86 of the projection of the
easy magnetization direction on the magnetic recording medium plane
and the recording track direction 84. The recording track direction
84 was along a line tangent to a recording track 87 that is
concentric with the disc-shaped magnetic recording medium 81. The
angle .alpha. between the easy magnetization direction and the
normal direction of the medium was fixed at 45.degree..
[0051] FIG. 9 plots the resolution against the angle .beta., and
FIG. 10 plots S/N against the angle .beta.. As shown in FIG. 9, the
resolution is highest in the range
0.degree..ltoreq..beta..ltoreq.20.degree.. While the resolution
monotonously decreased in the range 20.ltoreq..beta..ltoreq.13-
5.degree., it was better in the range
0.degree..ltoreq..beta..ltoreq.110.d- egree. than the resolution
when .alpha.=0.degree. shown in FIG. 5. FIG. 10 shows that S/N was
high in the range 0.degree..ltoreq..beta..ltoreq.70.de- gree..
Thus, it was revealed that both the resolution and S/N can be
improved in the range 0.degree..ltoreq..beta..ltoreq.70.degree.. It
can also be seen that the resolution and S/N are lower when
.beta.=180.degree. than when .beta.=0.degree.. When
.beta.=180.degree., the easy magnetization direction is inclined in
the opposite direction to the easy magnetization direction
according to the invention. Specifically, this is the case where,
when the easy magnetization direction is from the back surface of
the recording layer toward the upper surface thereof, and when the
recording track direction is from the upstream of the direction of
transportation of the medium toward the downstream thereof, the
direction of the projection of the easy magnetization direction on
the medium plane is antiparallel to the recording track direction.
This arrangement is preferable when recording an obliquely
evaporated tape using a ring head.
[0052] The reason why it is effective in the present invention to
reverse the direction of inclination of the easy magnetization
direction that is preferable in the combination of the obliquely
evaporated tape and a ring head is not clear. In the present
invention, the recording layer of the magnetic recording medium
includes a soft magnetic underlayer, as shown in FIG. 3, and,
during the write process, a steep magnetic field is applied
substantially along the normal direction of the medium from the
main pole of the SPT bead toward the soft magnetic underlayer
thereof. Presumably, these features of the present invention
combine to create an effect not found in the case of the
combination of a tape medium having no soft magnetic underlayer and
a ring head.
[0053] Thus, in accordance with the invention, both the resolution
and S/N can be improved when the angle .beta. between the direction
of the projection of the easy magnetization direction, inclined in
the opposite direction to that in the obliquely evaporated tape, on
the medium plane and the recording track direction is in the range
0.degree..ltoreq..beta.- .ltoreq.70.degree.. Particularly, a
greater improvement in resolution can be obtained when the range is
0.degree..ltoreq..beta..ltoreq.20.degree.. For example, when
.beta.=20.degree. and .alpha.=45.degree., the resolution can be
improved by a factor of 1.5 as compared with the case when
.alpha.=0.degree., that is when the easy magnetization direction is
along the normal direction of the magnetic recording medium. The
thermal stability of these two media, when expressed by the ratio
of reproduced output after 100 hours to that 10 seconds after
recording was 0.89 and 0.88, for the former and the latter,
respectively, thus showing little difference.
Embodiment 3
[0054] A magnetic recoding medium similar to the one in Embodiment
1 was produced. Films were formed by sputtering. During the
formation of a recording film, a mask plate for limiting the
direction of incoming particles was placed between a target and a
substrate, such that only particles traveling from a direction that
is inclined from the normal direction of the substrate toward one
direction were allowed to be deposited. The mask plate may be
either propeller-shaped or one having holes with their central axes
inclined with respect to the normal direction of the plate, for
example. In the present embodiment, the latter was used. FIG. 11
shows the arrangement of a target 111, a mask plate 112, and a
substrate 113, as well as a direction 114 of the incoming
particles. A uniform film was obtained by depositing a recording
film while rotating the target and the mask plate. A soft magnetic
underlayer was formed by a FeTaC layer of film thickness 400 nm. An
intermediate layer was formed by a NiTaZr layer of film thickness 5
nm. The recording film was formed by a CoCrPtB layer of film
thickness 20 nm. The intermediate film has the function of
improving the crystalinity and orientation of the recording film,
as well as preventing the atomic diffusion between the soft
magnetic underlayer and the recording film. On the surface of the
recording film was formed a carbon protective film of film
thickness 2 nm. The substrate temperature was set at 373 K and the
argon gas pressure during sputtering was set at 1 Pa. In the
present embodiment, the central axes of the holes in the mask plate
were inclined by 50.degree. with respect to the normal direction of
the plate, and the direction of the projection of each central axis
on the substrate plane was inclined to coincide with a line tangent
to the circumference of the substrate.
[0055] The crystalinity of the thus produced magnetic recording
medium was cross-sectionally observed with an electron microscope.
A sample was prepared from a small piece cut out from the medium in
a direction parallel to a tangent to its circumference. Observation
of the sample revealed the formation of columnar crystal particles
in a direction inclined away from the direction normal to the film
plane. The angle of inclination was about 45.degree.. The magnetic
recording medium was then cut into several small pieces. Then, the
torque curve concerning the rotation of magnetic field in a plane
containing the normal direction of the medium and the circumference
thereof was measured. Results indicated that the easy magnetization
direction was in a direction about 38.degree. away from the normal
direction of the medium on average. When the thus produced magnetic
recording medium was recorded and reproduced using an SPT head, the
resolution was improved by a factor of 1.3 and S/N by 2.6 dB as
compared with a perpendicular magnetic recording medium that was
produced without using a mask plate.
Embodiment 4
[0056] A magnetic recording medium similar to the one used in
Embodiment 2 was produced. The recording layer was formed by a
FePt-alloy nanoparticle medium. FePt is an intermetallic compound
having an L1.sub.0-type crystal structure that exhibits
ferromagnetism by ordering a disordered alloy with thermal
treatment. In the present embodiment, a soft magnetic underlayer
FeTaC was formed to a film thickness of 200 nm and an intermediate
layer of NiTaZr was formed to a film thickness of 4 nm on a
substrate by sputtering in advance. Then, a nanoparticle film
comprised of disordered alloy particles with an average particle
size of about 9 nm and an organic compound of oleic acid was formed
thereon.
[0057] As schematically shown in FIG. 12, while applying a parallel
magnetic field 122 to the substrate 121 from an external magnetic
field applying apparatus 125 and 126, the particles were irradiated
with an infrared laser 123 of wavelength 800 nm from an infrared
light irradiating apparatus 127. The particles were thus heated and
ordered such that their magnetic anisotropy was oriented in the
direction of the magnetic field. Immediately thereafter, the
substrate 121 was irradiated with an ultraviolet light 124 of
wavelength 200 nm from an ultraviolet light irradiating apparatus
128, so that the organic compound was cross-linked and the
particles were anchored, thus controlling the magnetic anisotropy.
The magnitude of the magnetic field was 10 kOe, and the direction
of its application was inclined by 60.degree. from the normal
direction of the medium. Where the infrared laser and the
ultraviolet light were irradiated, the direction of magnetic field
application as projected on the medium plane was 20.degree. off the
direction of the circumference of the medium. Irradiation was
conducted while rotating the medium and moving the irradiation
position along the radius, so that the entire surface could be
uniformly irradiated.
[0058] The resultant magnetic recording medium was cut into several
small pieces. A torque curve was measured by rotating the magnetic
field in a plane including the normal direction of the medium and
the direction rotated by 20.degree. from the direction of
circumference. The result revealed that the easy magnetization
direction was in a direction on average approximately 55.degree.
off the normal direction of the medium. Namely, in order to make
the easy magnetization direction of the medium 55.degree. off the
normal direction of the medium by the method of the present
embodiment, it was necessary to make the magnetization application
direction inclined from the normal direction of the medium by
60.degree.. In order to make the easy magnetization direction of
the medium 5.degree. off the normal direction of the medium, it was
sufficient to incline the magnetization application direction from
the normal direction of the medium by the same 5.degree.. Thus, in
order to manufacture a magnetic recording medium with the easy
magnetization direction ranging from 5.degree. to 55.degree. with
respect to the normal direction of the medium, the apparatus for
manufacturing the magnetic recording medium of the invention was
adapted such that it can vary the direction of magnetic field
application in the range between 5.degree. and 60.degree..
[0059] When the magnetic recording medium produced by the
above-described method was recorded and reproduced using an SPT
head, resolution was improved by a factor of 1.6 and S/N by 0.6 dB
as compared with a perpendicular magnetic recording medium in which
a magnetic field had been applied perpendicular to the medium plane
during manufacture.
[0060] Magnetic recording media were prepared by the same method
using different materials for the recording layer. To determine the
degree of improvement, the resolution and S/N of the media were
compared with those of perpendicular magnetic recording media using
the same materials in which the magnetic field was applied
perpendicular to the medium plane during preparation. The results
are shown in Table 1.
1TABLE 1 Comparison of improvements in resolution and S/N depending
on the recording layer material. Recording layer Ratio of
improvement Ratio of improvement material of resolution (-) of S/N
(dB) FePt 1.6 0.6 CoPt 1.3 0.3 CoPd 1.2 0.4 SmCo 1.2 0.5 FeNiPt 1.1
0.3 FeMnAl 1.1 0.0
Embodiment 5
[0061] In a magnetic recording apparatus utilizing a magnetic
recording medium similar to the one according to Embodiment 1, a
write-read head having a structure as schematically shown in FIG.
13 was employed. The head included a write head made up of a main
pole 131, an auxiliary pole 132, and a coil 133, and a read head
with a structure in which a magnetoresistive film 138 was
sandwiched between shields 139a and 139b. The head was disposed
opposite a magnetic recording medium having a recording layer 134
and a soft magnetic underlayer 135. When the recording track
direction was from the upstream of a direction 136 of
transportation of the medium to the downstream thereof, and when
the easy magnetization direction of the recording layer 134 was
from the back surface of the recording layer toward the upper
surface thereof, the direction of the projection of the easy
magnetization direction on the medium plane substantially coincided
with the direction of the recording tracks. As opposed to
Embodiment 1, the auxiliary pole 132 was disposed downstream of the
medium transportation direction 136 relative to the main pole 131.
A shield 137 made of a soft magnetic thin film was connected to the
auxiliary pole 132 and it extended to the vicinity of the main pole
131. FIG. 14 schematically shows the arrangement of the poles of
the head as seen from the air bearing surface (ABS), or the air
bearing surface of the magnetic head. As shown, the head is
characterized in that the shield 137 is wider than the edge of the
opposite main pole 131 downstream of the medium transportation
direction 136.
[0062] The write-read characteristics of the head with the thus
arranged magnetic poles when used for recording the same medium as
that of Embodiment 1 were estimated by computer simulation.
Computation conditions included an average particle size 12.7 nm of
the magnetic particles in the recording layer; recording layer
thickness 20 nm; magnetic anisotropic constant 1.3.times.10.sup.5
J/m.sup.3; saturation magnetization 0.314 T; underlayer thickness
100 nm; underlayer saturation flux density 1.2 T; underlayer
relative permeability 500; main pole width 160 nm; main pole
thickness 160 nm; head-medium magnetic spacing 15 nm; and
head-medium relative speed 20 m/s. In FIG. 14, the interval between
the main pole 131 and the shield 137 was 40 nm, the shield 137 was
4.9 .mu.m in width, 100 nm in thickness, and 2 .mu.m in length in
the direction of transportation of the medium. A low-density
recording with a bit length 152 nm and a high-density recording
with a bit length of 38 nm were carried out to determine the
resolution, which is the ratio, in percentage, of the high-density
output to the low-density output, and the S/N ratio, which is the
ratio, in dB, of the low-density output to the high-density noise.
The head magnetic field strength was 724 kA/m. The easy
magnetization direction and the medium transportation direction of
the magnetic recording medium used in this embodiment were the same
as those shown in FIG. 4.
[0063] FIG. 15 shows the resolution against angle .alpha.. FIG. 16
shows the S/N against angle .alpha.. The resolution was almost zero
when .alpha. was 0.degree.. Namely, it was revealed that the head
according to the present embodiment experienced difficulty
recording the perpendicular medium, in which the easy magnetization
direction exists in a vertical direction. However, as the easy
magnetization direction of the recording layer was inclined away
from the normal direction of the magnetic recording medium,
recording became possible. The resolution improved up to 18% or
more when .alpha..gtoreq.15.degree.. The S/N improved in the range
15.degree..ltoreq..alpha..ltoreq.55.degree. over that (17.9 dB; see
FIG. 6) of the case where the medium with .alpha.=0.degree. was
recorded using the conventional SPT head. Thus, it was revealed
that in accordance with the present embodiment, the S/N and
resolution can be improved when the angle .alpha. between the easy
magnetization direction and the normal direction of the medium was
in the range between 15.degree. and 55.degree..
[0064] The reason that no resolution was obtained in the range
0.ltoreq..alpha..ltoreq.15.degree. is presumably due to the
weakness of the head magnetic field strength. As shown in FIG. 7,
the required recording magnetic field against the angle .alpha.
exceeds the head magnetic field strength 724 kA/m of the present
embodiment in the range 0.degree..ltoreq..alpha..ltoreq.15.degree..
Thus, no saturation recording is possible in this range due to lack
of head magnetic field strength. It could be possible to achieve
saturation recording on a medium with
0.degree..ltoreq..alpha..ltoreq.15.degree. using the head of the
embodiment if the magnetic anisotropy of the medium is reduced to
thereby lower the required recording magnetic field. This is not
appropriate, however, as it could worsen thermal stability.
Accordingly, when the head of the present embodiment is used, the
range 15.degree..ltoreq..alpha..lt- oreq.55.degree. is appropriate.
For example, when .alpha.=45.degree., the resolution was as much as
36.8%, and S/N improved by 0.7 dB over that of the case where the
medium with .alpha.=0.degree. was recorded using the conventional
SPT head. Further, the thermal stability of the medium, when
expressed as the ratio of the reproduced output after 100 hours to
the reproduced output 10 seconds after end of recording, was 0.89
in both cases, irrespective of .alpha..
[0065] FIGS. 19 and 20 show modifications of the write-read head
with different auxiliary pole positions. Functional parts similar
to those of FIG. 13 are designated with similar numerals and will
not be described in detail. In the case of the magnetic head of
FIGS. 13 and 14, the auxiliary pole 132 is disposed downstream of
the medium transportation direction 136 relative to the main pole
131. In the magnetic heads of FIGS. 19 and 20, on the other hand,
auxiliary poles 192, 202a and 202b are positioned either upstream
or both upstream and downstream of the medium transportation
direction. Further, in the example of FIG. 19, a downstream shield
197 does not constitute a magnetic circuit, whereas a shield 207 in
the example of FIG. 20 constitutes a magnetic circuit. In the case
of FIG. 19, the length of the shield 197 in the medium
transportation direction should preferably be set large, between 3
to 5 .mu.m, for example. This head proved capable of providing
results similar to those described above.
Embodiment 6
[0066] In a magnetic recording apparatus similar to the one of
Embodiment 5, a medium with .alpha.=45.degree. was used and the
write-read characteristics of two kinds of head with different soft
magnetic thin-film shield shapes were estimated. FIGS. 17 and 18
each schematically show the shape of the main pole and the shield
as seen from the ABS surface (air bearing surface). In the head
shown in FIG. 17, a shield 173 extends to the side of a main pole
172. In the head shown in FIG. 18, a shield 183 surrounds the main
pole 182. Numerals 174 and 184 designate auxiliary poles and
numerals 171 and 181 indicate the medium transportation
direction.
[0067] The magnetic field strength at the center of the recording
layer of the magnetic recording medium decreased as the size of the
shield surrounding the main pole increased. While these heads
experienced difficulty recording a medium with .alpha.=0.degree.,
namely the perpendicular medium, in which the easy magnetization
direction is vertical, the heads successfully recorded when
combined with a medium with .alpha.=45.degree.. As compared with
the head of Embodiment 5, the head of FIG. 17 had reductions in
resolution by 7% and S/N by 1.1 dB. In the case of the head of FIG.
18, the reductions were 12% in resolution and 1.9 dB in S/N.
However, as compared with the head of Embodiment 5, the head of
FIG. 17 had a track width that was narrower by 15%, and the track
width of the head of FIG. 18 was narrower by 21%. Thus, it was
revealed that the heads of the present embodiment were suitable for
a narrow-track recording.
Embodiment 7
[0068] In a magnetic recording apparatus similar to the one of
Embodiment 5, when the easy magnetization direction was from the
back surface of the recording layer toward the front surface
thereof, and when the recording track direction was from the
upstream of the direction of transportation of the magnetic
recording medium toward the downstream thereof, the resolution and
S/N were estimated with varying angles .beta. between the direction
of the projection of the easy magnetization direction on the medium
plane and the recording track direction. The relationship between
the easy magnetization direction of the medium and its direction of
transportation was the same as that shown in FIG. 8. The shape of
the head was that of Embodiment 5 as shown in FIG. 14.
[0069] The resolution and S/N were estimated by the same computer
simulation as described above. As in Embodiment 5, recording is
difficult when .alpha.=0.degree., and recoding became possible as
the angle .alpha. increased. In this example, comparisons were made
at angles .beta.=0.degree., 90.degree. and 180.degree. when
.alpha.=45.degree.. As a result, it was revealed that the
resolution was highest at 36.8% when .beta.=0.degree.. It was 27.4%
when .beta.=90.degree., and 32.5% when .beta.=180.degree.. S/N was
18.7 dB when .beta.=0.degree., 17.4 dB when .beta.=90.degree., and
17.6 dB when .beta.=180.degree..
[0070] A case was also examined where .beta. was different for each
crystal particle forming the recording layer of the magnetic
recording medium. This means that, although .alpha.=45.degree. when
the magnetic recording medium was viewed as a whole, .beta. was
random. In this case too, recording was possible using the head of
the present embodiment, and the resolution was 23.7% and S/N was
18.1 dB. The head of the embodiment provided excellent resolution
with little deterioration in S/N regardless of the direction of
.beta.. This is presumably due to the very high recording magnetic
field gradient of the head. The head is not suitable for recording
the perpendicular magnetic recording medium with its easy
magnetization direction oriented in the direction of the normal
direction of the medium, because its magnetic field strength is
lower than that of the conventional SPT head in Embodiment 1.
However, the head can record magnetic recording media whose easy
magnetization direction is inclined from their normal direction,
and the feature of the head, that is the excellent recording
magnetic field gradient, can be fully exploited with that type of
media.
[0071] Thus, the magnetic recording medium according to the
invention comprises at least a recording layer in which the easy
magnetization direction is inclined from the normal direction of
the medium, and a soft magnetic underlayer. The inventive medium,
when information is recorded thereon using the SPT head, can
provide better resolution and S/N without adversely affecting its
thermal stability than the perpendicular magnetic recording medium,
in which the easy magnetization direction is parallel to the normal
direction of the medium. As a result, the invention can provide a
magnetic recording apparatus capable of providing an improved areal
density.
[0072] The invention provides a method of manufacturing a magnetic
recording medium, the method comprising the steps of:
[0073] forming a nanoparticle layer by disposing nanoparticles on a
substrate, the nanoparticles comprising alloy particles containing
at least one element selected from the group consisting of Fe, Co,
Ni, Mn, Sm, Pt, and Pd, wherein the alloy particles are coated with
an organic compound;
[0074] irradiating the nanoparticle layer with infrared light to
produce magnetic nanoparticles;
[0075] applying a magnetic field to the nanoparticle layer to
control the magnetization direction of the magnetic nanoparticles
in substantially one direction; and
[0076] irradiating the nanoparticle layer with ultraviolet light to
cross-link the organic compound, wherein
[0077] the angle formed by the direction of the magnetic field
applied in the magnetic field applying step and the direction
normal to the substrate is not less than 5.degree. and not more
than 60.degree..
[0078] The invention provides a magnetic recording medium
manufacturing apparatus comprising:
[0079] means for irradiating a nanoparticle layer disposed on a
substrate with infrared light to produce magnetic nanoparticles,
the nanoparticles comprising alloy particles containing at least
one element selected from the group consisting of Fe, Co, Ni, Mn,
Sm, Pt, and Pd, wherein the alloy particles are coated with an
organic compound;
[0080] means for applying a parallel magnetic field to the
nanoparticle layer, the magnetic field forming an angle of not less
than 5.degree. and not more than 60.degree. with the direction
normal to the substrate in order to control the direction of
magnetization of the magnetic particles in substantially one
direction;
[0081] means for applying ultraviolet light to the nanoparticle
layer to cross-link the organic compound; and
[0082] means for shifting the position of irradiation of the
infrared light and ultraviolet light on the substrate.
[0083] The invention provides a magnetic recording apparatus
comprising:
[0084] a magnetic recording medium;
[0085] a single pole type (SPT) head;
[0086] a slider on which the SPT head is mounted;
[0087] a suspension arm for securely fastening the slider; and
[0088] an actuator for supporting the suspension arm, wherein the
SPT head can be transported to an arbitrary position on the
recording medium by the movement of the actuator where it can
record information, and wherein
[0089] the SPT head comprises at least:
[0090] a main pole, an auxiliary pole, and a shield disposed
downstream of the direction of transportation of the medium with
respect to the main pole and having a wider width than the main
pole, wherein
[0091] the magnetic recording medium comprises at least a soft
magnetic underlayer and a recording layer, and wherein
[0092] the angle formed by the easy magnetization direction of the
recording layer and the direction normal to the medium is not less
than 15.degree. and not more than 55.degree..
* * * * *