U.S. patent application number 10/120402 was filed with the patent office on 2002-08-15 for magnetic recording disk, method of the magnetic recording disk and magnetic recording apparatus.
Invention is credited to Hosaka, Sumio, Inaba, Nobuyuki, Kirino, Fumiyoshi, Koyama, Eiji, Kuramoto, Hiroki, Naitou, Takashi, Takahashi, Ken, Terao, Motoyasu, Yamamoto, Hiroki.
Application Number | 20020110707 10/120402 |
Document ID | / |
Family ID | 11507884 |
Filed Date | 2002-08-15 |
United States Patent
Application |
20020110707 |
Kind Code |
A1 |
Kirino, Fumiyoshi ; et
al. |
August 15, 2002 |
Magnetic recording disk, method of the magnetic recording disk and
magnetic recording apparatus
Abstract
A magnetic recording medium includes a non-magnetic substrate,
an inorganic compound layer that is formed on the substrate and
which contains a crystalline first oxide and an amorphous second
oxide, and a magnetic layer that is formed on the inorganic
compound layer. The crystalline first oxide comprises at least one
oxide selected from cobalt oxide, chromium oxide, iron oxide and
nickel oxide. The amorphous second oxide comprises at least one
oxide selected from silicon oxide, aluminum oxide, titanium oxide,
tantalum oxide and zinc oxide. The amorphous second oxide is
present at a grain boundary of crystal grains of the first
oxide.
Inventors: |
Kirino, Fumiyoshi; (Tokyo,
JP) ; Inaba, Nobuyuki; (Hasuda, JP) ;
Takahashi, Ken; (Tokai, JP) ; Naitou, Takashi;
(Hitachiota, JP) ; Hosaka, Sumio; (Hinode, JP)
; Koyama, Eiji; (Tsuchiura, JP) ; Terao,
Motoyasu; (Hinode, JP) ; Yamamoto, Hiroki;
(Hitachi, JP) ; Kuramoto, Hiroki; (Yokohama,
JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
11507884 |
Appl. No.: |
10/120402 |
Filed: |
April 12, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10120402 |
Apr 12, 2002 |
|
|
|
09478377 |
Jan 6, 2000 |
|
|
|
6410133 |
|
|
|
|
Current U.S.
Class: |
428/835 ;
G9B/5.24; G9B/5.288 |
Current CPC
Class: |
G11B 5/7373 20190501;
G11B 5/656 20130101; G11B 5/7377 20190501; G11B 5/7371 20190501;
Y10S 428/90 20130101; Y10T 428/265 20150115; G11B 5/02 20130101;
G11B 5/012 20130101; G11B 2005/0002 20130101 |
Class at
Publication: |
428/694.0TS |
International
Class: |
G11B 005/738 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 7, 1999 |
JP |
11-001667 |
Claims
What is claimed is:
1. A magnetic recording medium comprising a nonmagnetic substrate,
an inorganic compound layer including a crystalline first oxide
having a hexagonal structure and an amorphous second oxide, said
inorganic compound layer being formed on the substrate, and a
magnetic layer formed on said inorganic compound layer, wherein
said crystalline first oxide comprises at least one oxide selected
from the group consisting of cobalt oxide, chromium oxide, iron
oxide and nickel oxide, said amorphous second oxide comprises at
least one oxide selected from the group consisting of silicon
oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc
oxide, and said amorphous second oxide is present at a grain
boundary of crystal grains of said first oxide.
2. The magnetic recording medium according to claim 1, wherein a
grain size of crystal grains constituting the first oxide is 10 nm
or less, and a spacing between crystal grains constituting the
first oxide is 0.5 nm-1.0 nm.
3. The magnetic recording medium according to claim 1, wherein an
average grain size of crystal grains constituting the magnetic
layer is 10 nm or less, and a standard deviations .sigma. of the
crystal grain size is 2 nm or less.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to magnetic recording
apparatuses having high performance and high reliability, magnetic
recording media for realizing the apparatuses and methods for
fabricating the same.
[0002] With recent remarkable development of a high
information-oriented society, multi-media which combine information
of various forms are rapidly spread. One of the information
recording apparatuses which support the rapid spread of multi-media
includes magnetic recording apparatuses such as magnetic recording
disks. At present, improvement in recording density and
miniaturization are attempted for magnetic recording disks.
Furthermore, reduction in price of magnetic recording disks is
being rapidly forwarded.
[0003] For realization of high density magnetic recording of
magnetic recording disks, the following are essential techniques:
(1) reduction of the spacing between the magnetic recording disk
and a magnetic head, (2) increase of coercivity of the magnetic
recording disks, and (3) new devising of signal processing
method.
[0004] Among them, as for the magnetic recording disks, in order to
realize a recording density exceeding 10 Gb/in.sup.2, it is
necessary to reduce the switching volume of magnetic layer occurs
as well as to increase the coercivity. For this purpose, magnetic
grains constituting the magnetic layer must be fine in their size.
Furthermore, in addition to the reduction of size of the magnetic
grains, uniformity in distribution of the size is important from
the viewpoint of thermal fluctuation. For the control of the size
of magnetic grains in the magnetic layer and the distribution of
the size, U.S. Pat. No. 4,652,499 proposes to provide a seed thin
layer under the magnetic layer.
SUMMARY OF THE INVENTION
[0005] However, in the conventional method, there is a limit in
control of crystal grain size and distribution of the crystal grain
size of the magnetic layer constituting the magnetic recording
disk, and fine grains and coarse grains coexist in the magnetic
layer. In the case of recording an information (in the case of
magnetic inversion), the magnetic layer in this state sometimes
cannot attain stable recording when ultrahigh density recording
higher than 10 Gb/in.sup.2 is carried out because of the influence
of leakage field from the surrounding magnetic grains or the
interaction with the large magnetic grains.
[0006] Accordingly, the first object of the present invention is to
provide a magnetic recording medium of high performance and low
noise by making finer the size of magnetic grains in the magnetic
layer. The second object of the present invention is to provide a
magnetic recording medium of low noise, low thermal fluctuation and
low thermal decay by controlling the distribution of the magnetic
grain size to become uniform. The third object of the present
invention is to provide a magnetic recording medium suitable for
high density magnetic recording by controlling the crystalographic
orientation of the magnetic layer. The fourth object of the present
invention is to provide a magnetic recording medium reduced in
magnetic inversion unit at the time of recording or erasion by
reducing magnetic interaction between magnetic grains. The fifth
object of the present invention is to provide a magnetic recording
medium capable of performing an ultra-high density magnetic
recording of higher than 10 Gb/in.sup.2.
[0007] The above objects can be attained by a magnetic recording
medium comprising a non-magnetic substrate, an inorganic compound
layer which is formed on the substrate and which contains a
crystalline first oxide (which is in the form of crystal grains
according to X-ray diffraction) comprising at least one oxide
selected from cobalt oxide, chromium oxide, iron oxide and nickel
oxide and a second oxide comprising at least one oxide selected
from silicon oxide, aluminum oxide, titanium oxide, tantalum oxide
and zinc oxide, said second oxide being present at grain boundary
of crystal grains of said first oxide, and a magnetic layer formed
on said inorganic compound layer.
[0008] Moreover, the inorganic compound layer preferably has such a
structure that the crystal grains of the first oxide have a
hexagonal honeycomb structure, the grains are two-dimensionally
regularly arranged, and the second oxide is present as amorphous
substance (measured to be amorphous according to X-ray diffraction)
at the crystal grain boundary of the first oxide. The crystal
grains of the first oxide are made fine, and distribution of the
size is nearly uniform. The crystal grains are most preferably
crystallographically oriented.
[0009] Orientation, crystal grain size and distribution of the
crystal grain size of the inorganic compound layer can be
controlled by optionally selecting the constituent material and the
concentration (composition) of the first oxide and the second oxide
or the conditions for the formation of the layer.
[0010] The inorganic compound layer formed on the substrate is
preferably of prismatic texture in which the crystal grains of the
first oxide grow in thickness direction of the layer. In this case,
thickness of the layer is preferably about 10-100 nm.
[0011] Furthermore, the inorganic compound layer made in platy form
can be used as a substrate. In this case, the crystal grains of the
first oxide preferably have a prismatic texture in thickness
direction.
[0012] When the magnetic layer is formed on the inorganic compound
layer, the magnetic layer is epitaxially grown from the crystal
grains in the inorganic compound layer. Since the amorphous second
oxide is precipitated at the grain boundary of the crystal grains
in the inorganic compound layer, the magnetic layer epitaxially
grows on the crystal grains and does not epitaxially grow on the
amorphous portion. Thus, the growing state of the magnetic layer on
the crystal grains differs from that on the amorphous crystal grain
boundary in the inorganic compound layer, resulting in variation of
orientation or texture of the magnetic layer. This variation causes
variation of magnetic properties, and the magnetic interaction
between the crystal grains constituting the magnetic layer can be
diminished.
[0013] Furthermore, the spacing between the crystal grains in the
inorganic compound layer can also be easily controlled by
controlling the composition of the compound. The magnetic
interaction between the magnetic crystal grains can be diminished
by the control of the spacing.
[0014] By diminishing the magnetic interaction between the crystal
grains constituting the magnetic layer, a zigzag pattern present in
the magnetic transition area can be made smaller. Specifically,
width of the zigzag pattern present in the magnetic transition area
of the track of the magnetic recording medium can be made less than
the gap length of a recording head. The width of the zigzag pattern
may not necessarily be smaller than the gap length along the whole
track, but it is ideal that the width is smaller than the gap
length along the whole track. The relation between the width of the
zigzag pattern and the gap length in this case is shown in FIG. 9.
In this way, noise of the magnetic recording media can be reduced.
Furthermore, since influence of noise can be made small even when
the width of the track is reduced, track density can be
lowered.
[0015] In order to perform smooth epitaxial growth, it is preferred
that the crystal structure of the crystal grains in the inorganic
compound layer is the same as or similar to the structure of the
magnetic grains constituting the magnetic layer. The term "similar
to" here means that the difference of lattice constant of the
crystal grains in the inorganic compound layer from that of the
magnetic grains constituting the magnetic layer is within the range
of .+-.10%. However, when the difference of lattice constant of the
crystal grains in the inorganic compound layer from that of the
magnetic grains constituting the magnetic layer is outside the
range of .+-.10%, a layer having a lattice constant which is middle
between both the lattice constants can be provided between the two
layers.
[0016] When the magnetic layer is epitaxially grown from the
inorganic compound layer as mentioned above, form and size of
crystal grains in the inorganic compound layer become nearly the
same as those in the magnetic layer. That is, the size of crystal
grains in the magnetic layer is determined by the size of crystal
grains in the inorganic compound layer. Therefore, the crystal
grains of the magnetic layer become fine and distribution of the
size becomes uniform. Specifically, the average grain size of the
crystal grains of the magnetic layer is preferably 10 nm or less,
and the distribution of the grain size is preferably 2 nm or less
in terms of standard deviation .sigma..
[0017] Furthermore, the crystal grains in the inorganic compound
layer are made fine and the distribution of the size is uniform,
and the grains are regularly arranged. Therefore, the crystal
grains of the magnetic layer formed thereon also become fine, and
the distribution of the size is uniform and can be controlled so
that the grains are regularly arranged. Accordingly, noise, thermal
fluctuation and thermal decay caused by the magnetic recording
media can be diminished.
[0018] By the above-mentioned techniques, magnetic inversion unit
and size thereof in magnetic recording media can be made small. The
magnetic inversion unit here is defined as follows. The minimum
unit of inversion is assumed to be one crystal grain of the
magnetic layer, and the number of units corresponding to the number
of the crystal grains of the magnetic layer when recording or
erasion is carried out is determined by observation with a magnetic
force microscope (MFM) or the like.
[0019] Here, it is preferred to use, as the magnetic layer, a
ferromagnetic thin layer of an alloy mainly composed of Co and
additionally containing Pt and at least one element selected from
Cr, Ta and Nb. Furthermore, in the structure of this ferromagnetic
thin layer, at least one element selected from Cr, Ta and Nb is
present in the form of segregation at the grain boundary of Co
crystal grains.
[0020] Moreover, there is provided a magnetic recording apparatus
comprising the magnetic recording medium, a driving part which
rotates the magnetic recording medium, a recording head comprising
a recording part and a read back part, and a means of moving the
recording head relative to the magnetic recording medium. Thus, a
magnetic recording apparatus can be realized which can perform high
density magnetic recording of higher than 10 Gb/in.sup.2,
furthermore, higher than 20 Gb/in.sup.2. In addition, various
information such as images, code data and audios are recorded in
this apparatus or read back from this apparatus, or the information
is erased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 shows a sectional structure of the magnetic recording
medium in Example 1 of the present invention.
[0022] FIG. 2 schematically shows the structure of the inorganic
compound layer.
[0023] FIG. 3 is a graph showing X-ray diffraction profile of the
magnetic layer.
[0024] FIG. 4 shows a sectional structure of the magnetic recording
medium in Example 2 of the present invention.
[0025] FIG. 5 is a graph showing X-ray diffraction profile of the
magnetic layer.
[0026] FIG. 6 shows a sectional structure of the magnetic recording
medium in Example 5 of the present invention.
[0027] FIG. 7A and FIG. 7B show construction of the magnetic
recording apparatus in the Example of the present invention.
[0028] FIG. 8 shows construction of the magnetic head.
[0029] FIG. 9 schematically shows a relation between width of
zigzag pattern and gap length.
[0030] In the drawings, 1 indicates a substrate, 2 indicates an
inorganic compound layer, 3 indicates a magnetic layer, 4 indicates
a protective layer, 5 indicates a lattice constant controlling
layer, and 10 indicates a magnetic recording medium.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The present invention will be explained in detail by way of
the following examples.
EXAMPLE 1
[0032] FIG. 1 shows the sectional structure of the magnetic
recording medium in Example 1 of the present invention. As
substrate 1, a glass substrate of 2.5' in diameter was used. An Al
or Al alloy substrate can also be used, and the size of the
substrate can also be changed. An inorganic compound layer 2 of 30
nm thick was formed on the substrate 1 by sputtering method using a
target comprising a sintered mixture of cobalt oxide (CoO) and
silicon oxide (SiO.sub.2) at 2:1. In carrying out the sputtering,
pure Ar was used as a discharge gas, discharge gas pressure was 3
mTorr, and applied DC power was 1 kW/150 mm.phi.. The substrate was
heated at 300.degree. C. during the sputtering.
[0033] The surface of the resulting inorganic compound layer 2 was
observed by TEM to find that crystal grains having honeycomb
structure of regular hexagon of 9 nm were regularly arranged as
shown in FIG. 2. The spacing between crystal grains 21 was 0.5-1.0
nm. The crystal grains 21 comprised cobalt oxide, and silicon oxide
was present at the grain boundary. The structure of the inorganic
compound layer 2 was observed by X-ray diffractometry to find that
the cobalt oxide was crystalline and the silicon oxide was
amorphous. Lattice constant of the crystal grains 21 was nearly
equal to that of Co.
[0034] The mixing ratio of CoO and SiO.sub.2 and the sputtering
conditions can be optionally selected. Furthermore, an oxide of a
metal differing in ion radius from Co (e.g., oxide of chromium,
iron or nickel) may be added to CoO.
[0035] A Co.sub.69Cr.sub.19Pt.sub.12 layer of 12 nm thick was
formed as a magnetic layer 3 on the inorganic compound layer 2 by
sputtering method. A Co--Cr--Pt alloy was used as a target in the
sputtering, and pure Ar was used as the discharge gas. The
discharge gas pressure was 3 mTorr and the applied DC power was 1
kW/150 mm.phi..
[0036] Finally, a carbon (C) layer of 5 nm thick was formed as a
protective layer 4 on the magnetic layer 3 to obtain a magnetic
recording medium 10. The sputtering conditions were pure Ar as the
discharge gas, 5 mTorr as the discharge gas pressure, and 1 kW/150
mm.phi. as the applied DC power density. A gas containing nitrogen
may be used in place of the Ar gas as the discharge gas. By using
this gas, C particles become fine and hence the resulting
protective layer is densified and the protection performance can be
improved.
[0037] The structure of the magnetic layer 3 was examined by X-ray
diffractometry and the results are shown in FIG. 3. As a result, it
can be seen that Co (102) was strongly oriented. The lattice
constant of the inorganic compound layer 2 and that of the magnetic
layer 3 were the same and 0.402 nm. When the surface (three
portions of 500.times.10 nm) of the magnetic layer 3 was observed
by an electron microscope, average grain size was 9 nm, and the
grain size distribution was 2 nm or less in standard deviation:
.sigma.. Thus, it can be seen that grains of the magnetic layer 3
became fine and distribution of the size was uniform. A section of
the magnetic recording medium was observed by an electron
microscope to find that the magnetic layer 3 epitaxially grew on
the inorganic compound layer 2, and crystal grains of the inorganic
compound layer and those of the magnetic layer 3 had the same size.
Moreover, both the inorganic compound layer 2 and the magnetic
layer 3 had prismatic crystal structure and size of the crystal
grains did not change.
[0038] Next, magnetic properties of the magnetic layer 3 were
measured to obtain a coercivity of 3.5 kOe, an Isv of
2.5.times.10.sup.-16 emu, an S of 0.8 which is indication for
squareness of hysteresis at M-H loop, and an S* of 0.86, and thus
it had good magnetic properties. From the above, it can be seen
that crystal grain size of the magnetic layer was small and the
distribution of the size was uniform.
[0039] Furthermore, a lubricant was coated on the surface of the
magnetic recording medium 10, and this was incorporated in a
magnetic recording and read back apparatus, and read/write
characteristics were evaluated.
[0040] FIG. 7A and FIG. 7B show a plan view and a sectional view of
the magnetic recording apparatus of the present invention,
respectively. This is a magnetic recording system comprising a
magnetic recording medium 74, a driving part 75 which rotates the
magnetic recording medium 74, a magnetic head 71 for read/write to
the magnetic recording medium 74, a driving part 72 which moves the
magnetic head 71 relative to the magnetic recording medium 74, and
a read/write signal processing means 73 for signal input to the
magnetic head 71 and read back of output signal from the magnetic
head 71.
[0041] As shown in FIG. 8, magnetic head 71 comprises read back
head 81 and recording head 82. The recording head 82 has upper
magnetic core 85, lower magnetic core 83 and gap layer 84. A soft
magnetic layer having a highly saturated magnetic flux density of
2.1 T was used as the gap layer 84 of the recording head 82, and
the gap length was 0.15 .mu.m. A magnetic head having a giant
magnetoresistive effect was used as the read back head 81. The
distance between the surface of the magnetic head 71 facing the
medium and the magnetic layer of the magnetic recording medium 74
was 20 nm. When a signal corresponding to 20 Gb/in.sup.2 was
recorded in the magnetic recording medium to evaluate S/N, a read
output of 32 dB was obtained. A magnetic inversion unit of the
magnetic layer was measured by a magnetic force microscope (MFM) to
find that this was about 2 to 3 grains and sufficiently small.
Furthermore, the area in which zigzag pattern of the magnetic
transition region was present was 0.1 .mu.m measured by a magnetic
force microscope (MFM), which was less than the gap length of the
magnetic head and extremely small. Moreover, thermal fluctuation
and thermal decay did not occur. This is due to the small
distribution of crystal grain size of the magnetic layer. When
error rate of this magnetic recording medium was measured, it was
1.times.10.sup.-5 or less in terms of the value when signal
processing was not conducted.
[0042] In this example, cobalt oxide was used as crystal grains of
the inorganic compound layer, but grains of the magnetic layer can
also be made fine and distribution of the size can be made uniform
by using chromium oxide, iron oxide or nickel oxide as the crystal
grains. Furthermore, it is also possible to allow aluminum oxide,
titanium oxide, tantalum oxide or zinc oxide to be present at the
crystal grain boundary.
[0043] Moreover, magnetic recording media shown in the following
examples can also be applied to such magnetic recording
apparatus.
EXAMPLE 2
[0044] FIG. 4 shows the sectional structure of the magnetic
recording medium in Example 2 of the present invention. As the
substrate, a glass substrate of 2.5" in diameter was used. An
inorganic compound layer 2 of 30 nm thick was formed on the
substrate 1 by sputtering method using a target comprising a
sintered mixture of cobalt oxide (CoO) and zinc oxide (ZnO) at 3:1.
The above thickness was such that no peeling from the substrate
occurs, taking into consideration the internal stress of the whole
magnetic recording medium. For the sputtering, pure Ar was used as
a discharge gas, and the discharge gas pressure was 3 mTorr and the
applied DC power was 1 kW/150 mm.phi.. The substrate was heated at
300.degree. C. during the sputtering. The surface of the resulting
inorganic compound layer 2 was observed by TEM to find that the
surface had a honeycomb structure comprising regular hexagon
crystal grains of 10 nm in diameter and amorphous zinc oxide was
present at the crystal grain boundary. Lattice constant of the
crystal grains of cobalt oxide was larger 20% than that of the
magnetic layer 3. It can be seen that size and lattice constant of
crystal grains of cobalt oxide changed with changing the amorphous
substance present at the grain boundary from silicon oxide in
Example 1 to zinc oxide in Example 2. As a result of .mu.-EDX
analysis, it was found that this was because the amorphous
substance was dissolved in the crystal grains in the state of a
solid solution.
[0045] Therefore, in this example, a Cr.sub.85Ti.sub.15 alloy thin
layer of 50 nm thick was formed as a lattice constant controlling
thin layer 5 having a lattice constant middle between that of the
inorganic compound layer 2 and that of the magnetic layer 3 prior
to the formation of the magnetic layer 3. Since the lattice
constant controlling thin layer 5 can optionally select the lattice
constant by controlling the Ti concentration, the difference in
lattice constant between the inorganic compound layer 2 and the
magnetic layer 3 can be controlled to 10% or less. The lattice
constant controlling thin layer 5 was formed by sputtering method
using a Cr--Ti alloy target. For the sputtering, pure Ar was used
as a discharge gas, and the discharge gas pressure was 3 mTorr and
the applied DC power was 1 kW/150 mm.phi..
[0046] As magnetic layer 3, a Co.sub.69Cr.sub.19Pt.sub.12 layer of
12 nm thick was formed on the lattice constant controlling thin
layer 5 by sputtering method. For the sputtering, a Co--Cr--Pt
alloy target was used, pure Ar was used as a discharge gas, and the
discharge gas pressure was 3 mTorr and the applied DC power was 1
kW/150 mm.phi..
[0047] Finally, a carbon (C) layer of 5 nm thick was formed as a
protective layer 4 by sputtering method to obtain a magnetic
recording medium 10. For the sputtering, pure Ar was used as the
discharge gas, the discharge gas pressure was 5 mTorr, and the
applied DC power was 1 kW/150 mm.phi.. A gas containing nitrogen
may be used in place of the Ar gas as the discharge gas, and in
this case, C particles become fine and hence the resulting
protective layer is densified and the protection performance can be
improved.
[0048] The structure of the magnetic layer 3 was examined by X-ray
diffractometry and the results are shown in FIG. 5. From FIG. 5, it
can be seen that Co (102) was strongly oriented.
[0049] When the surface of the magnetic layer 3 was observed by an
electron microscope, average grain size was 8 nm, and the grain
size distribution was 3 or less in terms of .sigma.. Thus, it can
be seen that crystal grains of the magnetic layer 3 became fine and
distribution of the size was uniform. A section of the magnetic
recording medium was observed by an electron microscope to find
that the crystal grains of the inorganic compound layer 2 and the
magnetic layer 3 epitaxially grew. Moreover, crystal grains of both
the inorganic compound layer 2 and the magnetic layer 3 had
prismatic crystal structure and size of the crystal grains did not
change.
[0050] Furthermore, magnetic properties of the magnetic layer 3
were measured. The magnetic properties obtained were a coercivity
of 4.0 kOe, an Isv of 2.5.times.10.sup.-16 emu, an S of 0.81 which
is indication for squareness of hysteresis at M-H loop, and an S*
of 0.85, and thus it had good magnetic properties.
[0051] Next, a lubricant was coated on the surface of the magnetic
recording medium 10, and read/write characteristics were evaluated
in the same manner as in Example 1. When a signal corresponding to
20 GB/in.sup.2 was recorded in the magnetic recording medium to
evaluate S/N, a read output of 32 dB was obtained. A magnetic
inversion unit of the magnetic layer was measured by a magnetic
force microscope (MFM) to find that this was about 2 to 3 grains
and sufficiently small. Furthermore, the area in which zigzag
pattern of the magnetic transition region was present was 0.1
.mu.m, which was less than the gap length (0.15 .mu.m)of the
recording head and extremely small. Moreover, thermal fluctuation
and thermal decay did not occur. When failure rate of this magnetic
recording medium was measured, it was 1.times.10.sup.-5 or less in
terms of the value when signal processing was not conducted.
EXAMPLE 3
[0052] Example 3 illustrates an example of controlling the lattice
constant of crystal grains of cobalt oxide without using the
lattice constant controlling thin layer.
[0053] First, as substrate 1, a glass substrate of 2.5" in diameter
was used. An inorganic compound layer 2 of 30 nm thick was formed
on the substrate 1 by simultaneous sputtering method using a binary
target comprising a target of a sintered mixture of CoO and
Fe.sub.2O.sub.3 at 3:1 and a target of ZnO. Applied power was
adjusted so that the respective targets were sputtered at 2:1. For
the sputtering, pure Ar was used as a discharge gas, and the
discharge gas pressure was 3 mTorr. The sputtering was conducted at
room temperature. The surface of the resulting inorganic compound
layer 2 was observed by TEM to find that crystal grains having
honeycomb structure of regular hexagon of 9 nm were regularly
arranged as in Example 1. The spacing between crystal grains was
0.5-1.0 nm. Iron was present in the space between the crystal
grains of cobalt oxide, and silicon oxide was present at the grain
boundary. Observation by X-ray diffractometry shows that the cobalt
oxide was crystal grains and the silicon oxide was amorphous.
Lattice constant was nearly equal to that of Co which was a main
component of the magnetic layer.
[0054] In Example 2, the lattice constant of the magnetic layer
differed from that of crystal grains of cobalt oxide in the
inorganic compound layer. However, lattice constant of the crystal
grains in the inorganic compound layer can be controlled by adding
iron oxide to cobalt oxide, and can be made nearly equal to that of
the magnetic layer.
[0055] Further, a Co.sub.69Cr.sub.19Pt.sub.12 layer of 12 nm thick
was formed as a magnetic layer 3 on the inorganic compound layer 2
by sputtering method. A Co--Cr--Pt alloy was used as a target in
the sputtering, and pure Ar was used as the discharge gas. The
discharge gas pressure was 3 mTorr and the applied DC power was 1
kW/150 mm.phi.. The substrate was heated at 300.degree. C. during
the sputtering.
[0056] Finally, a C layer of 5 nm thick was formed as a protective
layer 4 by sputtering method to obtain a magnetic recording medium.
For the sputtering, the discharge gas was pure Ar, the discharge
gas pressure was 5 mTorr, and the applied DC power was 1 kW/150
mm.phi..
[0057] Next, the structure of the magnetic layer 3 was examined by
X-ray diffractometry and the results are shown in FIG. 3. As a
result, it can be seen that Co (102) was strongly oriented. The
lattice constant of the inorganic compound layer 2 and that of the
magnetic layer 3 were nearly the same and 0.402 nm. When the
surface of the magnetic layer was observed by an electron
microscope, average grain size was 9 nm, and the grain size
distribution was 2 nm or less in standard deviation: .sigma.. Thus,
it can be seen that the crystal grains of the magnetic layer 3
became fine and the distribution of the size was uniform. A section
of the magnetic recording medium was observed by an electron
microscope to find that the inorganic compound layer and the
magnetic layer epitaxially grew, and the crystal grains had the
same size. Moreover, the crystal grains of both the inorganic
compound layer and the magnetic layer had prismatic structure and
size of the crystal grains did not change.
[0058] Furthermore, magnetic properties of the magnetic layer were
measured. The magnetic properties obtained were a coercivity of 3.5
kOe, an Isv of 2.5.times.10.sup.-16 emu, an S of 0.8 which is
indication for squareness of hysteresis at M-H loop, and an S* of
0.86, and thus it had good magnetic properties. This is because the
crystal grains of the magnetic layer were fine and the size
distribution was uniform.
[0059] Next, a lubricant was coated on the surface of the magnetic
recording medium 10, and read/write characteristics were evaluated
in the same manner as in Example 1. When a signal corresponding to
20 Gb/in.sup.2 was recorded in the magnetic recording medium to
evaluate S/N, a read output of 32 dB was obtained. A magnetic
inversion unit of the magnetic layer was measured by a magnetic
force microscope (MFM) to find that this was about 2 to 3 grains
and sufficiently small. Furthermore, the area in which zigzag
pattern of the magnetic transition region was present was 0.1
.mu.m, which was less than the gap length (0.15 .mu.m)of the
recording head and extremely small. Moreover, thermal fluctuation
and thermal decay did not occur. When failure rate of this magnetic
recording medium was measured, it was 1.times.10.sup.-5 or less in
terms of the value when signal processing was not conducted.
EXAMPLE 4
[0060] Example 4 illustrates an example where spacing between
crystal grains was controlled by suitably selecting the amorphous
substance in the inorganic compound layer.
[0061] As substrate 1, a glass substrate of 2.5" in diameter was
used. An inorganic compound layer 2 of 30 nm thick was formed on
the substrate 1 by simultaneous binary sputtering method using two
targets of a sintered cobalt oxide (CoO) and a sintered mixture of
SiO.sub.2 and TiO.sub.2 at 3:1. For the sputtering, pure Ar was
used as a discharge gas, and the discharge gas pressure was 3
mTorr. Applied RF power was adjusted so that the CoO target and the
SiO.sub.2-TiO.sub.2 target were sputtered at 2:1.
[0062] The surface of the resulting inorganic compound layer 2 was
observed by TEM to find that it had a honeycomb structure in which
crystal grains of regular hexagon of 9 nm were regularly arranged
as in FIG. 2. Furthermore, analysis by .mu.-EDX showed that the
crystal grains comprised cobalt oxide, and the silicon oxide
present at crystal grain boundary was amorphous. The spacing
between crystal grains was 1 nm. This spacing could be controlled
by changing the ratio of SiO.sub.2 and TiO.sub.2. Moreover, the
spacing between the crystal grains could be extended to about 2-3
nm by using zinc oxide in place of TiO.sub.2.
[0063] Next, a Co.sub.69Cr.sub.19Pt.sub.12 layer of 12 nm thick was
formed as a magnetic layer 3 on the inorganic compound layer 2 by
sputtering method. A Co--Cr--Pt alloy was used as a target in the
sputtering, and pure Ar was used as the discharge gas. The
discharge gas pressure was 3 mTorr and the applied DC power was 1
kW/150 mm.phi.. The substrate was heated at 300.degree. C. during
the sputtering.
[0064] Finally, a C layer of 5 nm thick was formed as a protective
layer 4 by sputtering method to obtain a magnetic recording medium.
For the sputtering, the discharge gas was Ar, the discharge gas
pressure was 5 mTorr, and the applied DC power was 1 kW/150
mm.phi..
[0065] Next, the structure of the inorganic compound layer was
examined by X-ray diffractometry to find a diffraction peak at
around 2.theta.=62.50 corresponding to CoO(220). No other clear
peaks were observed. A very broad peak was observed at around
20.theta.=44.degree., and it is considered that this is because of
overlapping of a peak caused by the glass substrate and a peak
caused by the amorphous substance at the grain boundary.
[0066] Further, the structure of the magnetic layer was examined by
X-ray diffractometry to find that Co(102) was strongly oriented.
This is reflective of the fact that CoO(220) was oriented in the
inorganic compound layer, and shows that the magnetic layer
epitaxially grew on the inorganic compound layer. The orientation
of Co in the magnetic layer is suitable for high density
recording.
[0067] When the surface of the magnetic layer was observed by an
electron microscope, average grain size (nearly circular) was 10
nm, and the grain size distribution was 1.5 nm or less in terms of
standard deviation: .sigma. and was very small. As compared with a
magnetic recording medium in which the inorganic compound layer was
not formed, Co(102) plane was not observed in the comparative
medium. Thus, it can be seen that the inorganic compound layer of
the present invention greatly contributes to control of orientation
of the magnetic layer.
[0068] Observation of a section of the magnetic recording medium
showed that the magnetic layer epitaxially grew on the inorganic
compound layer. Moreover, it can be seen that the crystal grains of
both the inorganic compound layer and the magnetic layer had
prismatic structure and the size of the crystal grains did not
change. Moreover, spacing between crystal grains of the inorganic
compound layer 2 was 1.0 nm, and it can be seen that since the
magnetic layer epitaxially grew on the crystal grains of the
inorganic compound layer, the crystal grains of the magnetic layer
were physically isolated from each other. As a result, there is the
effect that magnetic interaction between the crystal grains of the
magnetic layer can be diminished.
[0069] Next, magnetic properties of the magnetic layer were
measured. The magnetic properties obtained were a coercivity of 3.5
kOe, an Isv of 2.5.times.10.sup.-16 emu, an S of 0.8 which is an
indication for squareness of hysteresis at M-H loop, and an S* of
0.86, and thus it had good magnetic properties. This is because the
crystal grains of the magnetic layer were fine and the size
distribution was uniform.
[0070] Next, a lubricant was coated on the surface of the magnetic
recording medium 10, and read/write characteristics were evaluated
in the same manner as in Example 1. When a signal corresponding to
20 Gb/in.sup.2 was recorded in the magnetic recording medium to
evaluate S/N, a read output of 32 dB was obtained. A magnetic
inversion unit of the magnetic layer was measured by a magnetic
force microscope (MFM) to find that this was about 2 to 3 grains
and was sufficiently small. Furthermore, the area in which zigzag
pattern of the magnetic transition region was present was 0.1
.mu.m, which was less than the gap length (0.15 .mu.m) of the
magnetic head and was extremely small. Moreover, thermal
fluctuation and thermal decay did not occur. When failure rate of
this magnetic recording medium was measured, it was
1.times.10.sup.-5 or less in terms of the value obtained when
signal processing was not conducted.
EXAMPLE 5
[0071] Example 5 illustrates an example where a disk substrate was
formed using the inorganic compound layer of the present
invention.
[0072] A sectional structure of the magnetic recording medium in
Example 5 is shown in FIG. 6.
[0073] First, an inorganic compound layer in which amorphous
silicon oxide (SiO.sub.2) was present at grain boundary of cobalt
oxide (CoO) crystal grains was employed as substrate 11. A section
of the resulting substrate was observed by TEM to find that it had
a honeycomb structure in which crystal grains of regular hexagon of
10 nm were regularly arranged, and the spacing between crystal
grains was 0.5-1.0 nm. Observation of a section of the inorganic
compound layer showed a prismatic structure as shown in FIG. 6.
[0074] A Co.sub.69Cr.sub.19Pt.sub.12 layer of 12 nm thick was
formed as a magnetic layer 3 on the substrate 11 by sputtering
method. A Co--Cr--Pt alloy was used as a target in the sputtering,
and pure Ar was used as the discharge gas. The discharge gas
pressure was 3 mTorr and the applied DC power was 1 kW/150 mm.phi..
The substrate 11 was heated at 300.degree. C. during the
sputtering.
[0075] Finally, a C layer of 5 nm thick was formed as a protective
layer 4 by sputtering method to obtain a magnetic recording medium.
For the sputtering, the discharge gas was Ar, the discharge gas
pressure was 5 mTorr, and the applied DC power was 1 kW/150
mm.phi..
[0076] Further, the structure of the magnetic layer was examined by
X-ray diffractometry to find that Co(102) was strongly oriented as
in Example 1. When the surface of the magnetic layer was observed
by an electron microscope, average grain size was 10 nm, and the
grain size distribution was 2 nm or less in terms of standard
deviation: .sigma.. Observation of a section of the layer showed
that the magnetic layer 3 epitaxially grew on the substrate 11 of
the inorganic compound layer, and the crystal grains of both the
layers had nearly the same size. Furthermore, the crystal grains of
the substrate 11 of the inorganic compound layer and the magnetic
layer 3 had prismatic structure and the size of the crystal grains
did not change.
[0077] Magnetic properties of the magnetic layer were measured. The
magnetic properties obtained were a coercivity of 3.5 kOe, an Isv
of 2.5.times.10.sup.-16 emu, an S of 0.8 which is an indication for
squareness of hysteresis at M-H loop, and an S* of 0.86, and thus
it had good magnetic properties. This is because the crystal grains
of the magnetic layer were fine and the size distribution was
uniform.
[0078] Next, a lubricant was coated on the surface of the magnetic
recording medium 10, and read/write characteristics were evaluated
in the same manner as in Example 1. When a signal corresponding to
20 Gb/in.sup.2 was recorded in the magnetic recording medium to
evaluate S/N, a read output of 32 dB was obtained. A magnetic
inversion unit of the magnetic layer was measured by a magnetic
force microscope (MFM) to find that this was about 2 to 3 grains
and was sufficiently small. Furthermore, the area in which zigzag
pattern of the magnetic transition region was present was 0.1
.mu.m, which was less than the gap length (0.15 .mu.m) of the
magnetic head and was extremely small. Moreover, thermal
fluctuation and thermal decay did not occur. When failure rate of
this magnetic recording medium was measured, it was
1.times.10.sup.-5 or less in terms of the value obtained when
signal processing was not conducted.
[0079] According to the present invention, crystal grains of a
magnetic layer can be made fine and crystal grain size distribution
can be small by epitaxially growing the magnetic layer on an
inorganic compound layer small in crystal grain size distribution.
Thus, magnetic recording media low in noise and diminished in
thermal fluctuation and thermal decay can be realized.
[0080] Moreover, since control of crystal orientation of the
magnetic layer is possible, the magnetic layer can have an
orientation suitable for high density magnetic recording.
[0081] Furthermore, spacing between crystal grains of the magnetic
layer can be controlled, and, hence, interaction between the
crystal grains of the magnetic layer can be reduced. As a result,
magnetic recording media of low noise and fine magnetic domains can
be obtained and high density recording becomes possible.
* * * * *