U.S. patent application number 12/969351 was filed with the patent office on 2011-06-23 for perpendicular magnetic recording medium, manufacturing process of the same, and magnetic recording/reproducing apparatus using the same.
This patent application is currently assigned to Hitachi Global Storage Technologies Netherlands B.V.. Invention is credited to Reiko Arai, Yoshinori Honda, Mineaki Kodama, Kiwamu Tanahashi.
Application Number | 20110151144 12/969351 |
Document ID | / |
Family ID | 35187459 |
Filed Date | 2011-06-23 |
United States Patent
Application |
20110151144 |
Kind Code |
A1 |
Arai; Reiko ; et
al. |
June 23, 2011 |
PERPENDICULAR MAGNETIC RECORDING MEDIUM, MANUFACTURING PROCESS OF
THE SAME, AND MAGNETIC RECORDING/REPRODUCING APPARATUS USING THE
SAME
Abstract
Embodiments of the invention provide a perpendicular magnetic
recording medium improved for fly ability, high in read signal
quality, and capable of suppressing magnetic decay of recorded
magnetization to be caused by stray fields. In one embodiment, a
perpendicular recording layer is formed over a substrate with a
soft magnetic underlayer therebetween, then an amorphous or
nano-crystalline layer is formed between the substrate and the soft
magnetic underlayer. The soft magnetic underlayer includes first
and second amorphous soft magnetic layers, as well as a nonmagnetic
layer formed between those first and second amorphous soft magnetic
layers. The first and second amorphous soft magnetic layers are
given uniaxial anisotropy in the radial direction of the substrate
respectively and coupled with each other antiferromagnetically.
Inventors: |
Arai; Reiko; (Kanagawa,
JP) ; Tanahashi; Kiwamu; (Tokyo, JP) ; Honda;
Yoshinori; (Kanagawa, JP) ; Kodama; Mineaki;
(Kanagawa, JP) |
Assignee: |
Hitachi Global Storage Technologies
Netherlands B.V.
Amsterdam
NL
|
Family ID: |
35187459 |
Appl. No.: |
12/969351 |
Filed: |
December 15, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11107588 |
Apr 15, 2005 |
7875371 |
|
|
12969351 |
|
|
|
|
Current U.S.
Class: |
427/599 ;
977/890 |
Current CPC
Class: |
G11B 5/66 20130101; G11B
5/84 20130101; G11B 5/667 20130101; G11B 5/852 20130101 |
Class at
Publication: |
427/599 ;
977/890 |
International
Class: |
G11B 5/852 20060101
G11B005/852; B05D 3/00 20060101 B05D003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 2004 |
JP |
2004-120754 |
Claims
1.-11. (canceled)
12. A method for manufacturing a perpendicular magnetic recording
medium, comprising: forming an amorphous layer or nano-crystalline
layer over a substrate; forming a first amorphous soft magnetic
layer on said amorphous layer or nano-crystalline layer; cooling
said substrate while applying a magnetic field to said substrate in
a radial direction thereof; and forming a nonmagnetic layer on said
first amorphous soft magnetic layer; forming a second amorphous
soft magnetic layer on said nonmagnetic layer; forming a
perpendicular recording layer on said second amorphous soft
magnetic layer.
13. The method according to claim 12, wherein cooling said
substrate while applying a magnetic field to said substrate in the
radial direction thereof is provided just after forming said second
amorphous soft magnetic layer.
14. The method according to claim 12, wherein said substrate is
cooled under 100.degree. C. in said step of cooling.
15. The method according to claim 12, wherein said first and second
amorphous soft magnetic layers are given uniaxial anisotropy in the
radial direction of said substrate respectively and coupled with
each other antiferromagnetically.
16. A method for manufacturing a perpendicular magnetic recording
medium, comprising: forming an amorphous layer or nano-crystalline
layer over a substrate; forming a first amorphous soft magnetic
layer on said amorphous layer or nano-crystalline layer; forming a
nonmagnetic layer on said first amorphous soft magnetic layer;
forming a second amorphous soft magnetic layer on said nonmagnetic
layer; cooling said substrate while applying a magnetic field to
said substrate in a radial direction thereof; and forming a
perpendicular recording layer on said second amorphous soft
magnetic layer.
17. The method according to claim 16, wherein said nonmagnetic
layer is formed between ferromagnetic layers.
18. The method according to claim 16, wherein said nonmagnetic
layer contains an alloy made of a nonmagnetic material and a
ferromagnetic material.
19. The method according to claim 16, wherein cooling said
substrate while applying a magnetic field to said substrate in a
radial direction thereof is provided just after forming said first
amorphous soft magnetic layer.
20. The method according to claim 16, wherein said substrate is
cooled under 100.degree. C. in said step of cooling.
21. The method according to claim 16, wherein said first and second
amorphous soft magnetic layers are given uniaxial magnetic
anisotropy in the radial direction of said substrate respectively
and coupled with each other antiferromagnetically.
22.-25. (canceled)
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority from Japanese Patent
Application No. JP2004-120754, filed Apr. 15, 2004, the entire
disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a magnetic recording medium
and a magnetic recording/reproducing apparatus, particularly to a
perpendicular magnetic recording medium having high recording
density and a method for manufacturing the same, as well as a
magnetic recording/reproducing apparatus that uses the same.
[0003] In recent years, the areal recording density of respective
magnetic disk drives is being expanded by 100% annually. As the
areal recording density is increased such way, however, a problem,
so-called thermal decay of magnetization, has come to appear. This
is why the conventional longitudinal magnetic recording is
considered to be difficult to achieve the areal recording density
over 7.75 gigabits.
[0004] On the other hand, unlike the conventional longitudinal
magnetic recording, the perpendicular recording is characteristic
in that the demagnetizing field that works between adjacent bits
decreases in proportion to an increase of the linear recording
density, whereby the recorded magnetization is stabilized. In
addition, because a soft magnetic underlayer having high magnetic
permeability is provided under the subject perpendicular recording
layer to obtain a strong recording magnetic field, the coercivity
of the perpendicular recording layer can be increased.
Consequently, the perpendicular recording is now under examination
as a recording method expected to overstep the limit of the thermal
fluctuation of the conventional longitudinal recording.
[0005] One of the effective methods for realizing such high density
recording with use of the perpendicular recording method is
combining a double-layer perpendicular recording medium consisting
of a soft magnetic underlayer and a perpendicular recording layer
with a single pole type head. However, the double-layer
perpendicular recording medium has been confronted with a problem;
the medium includes a soft magnetic underlayer having high
saturation flux density (Bs) and therefore, the following three
points (1) to (3) are required to be improved to solve the problem.
(1) The leakage magnetic flux from the magnetic domain wall of the
soft magnetic layer is observed as spike noise. (2) The magnetic
domain wall of the soft magnetic underlayer moves, whereby decay of
magnetization occurs in the recorded magnetization. (3) Stray
fields in the apparatus are concentrated at the recording head,
whereby decay of magnetization occurs in the recorded magnetization
just under the recording head.
[0006] Furthermore, because the soft magnetic underlayer is as
thick as several tens of nanometers to several hundreds of
nanometers, the surface smoothness of the underlayer is lost and
this might affect the forming of the perpendicular recording layer
and the fly ability of the recording head adversely.
[0007] One of the methods proposed for solving such a problem is,
as disclosed in the official gazettes of JP-A Nos. 129946/1995 and
191217/1999, to provide a hard magnetic pinning layer between the
soft magnetic layer and the substrate and orient the magnetization
of the underlayer in one direction. The official gazette of JP-A
No. 103553/1994 also proposes a method for suppressing the domain
wall motion of the soft magnetic underlayer through exchange
coupling with the anti-ferromagnetic in which magnetic spinning is
oriented in one direction. In addition, the official gazette of
JP-A No. 155321/2001 discloses another method, which reverses the
orientation of the magnetization of the soft magnetic layer by
forming the soft magnetic layer with two or more layers separated
by a nonmagnetic layer respectively.
BRIEF SUMMARY OF THE INVENTION
[0008] However, the method for providing the hard magnetic pinning
layer might cause a problem; a magnetic domain is easily formed at
the inner and outer edges of the subject disk respectively and
spike noise is observed around those edges. On the other hand, the
method for using the anti-ferromagnetic layer to suppress the
domain wall motion of the soft magnetic layer is effective to
suppress the decay of magnetization to be caused by the domain wall
motion in the recorded magnetization, but it might not suppress the
spike noise to be caused by the domain wall. Further, the method
for reversing the magnetization of the laminated soft magnetic
layer is effective to suppress the spike noise and the decay of
magnetization in the recorded magnetization, and improve the stray
field robustness. However, the method is apt to enable each layer
to take a multi-domain structure if the substrate is a disk-shaped
one, so that modulation might be observed in output signals. Any of
those methods cannot solve the above problems that obstruct
achievement of the surface smoothness of the soft magnetic
underlayer, the fly ability of the recording head, etc.
[0009] Under such circumstances, it is a feature of the present
invention to provide a perpendicular magnetic recording medium
capable of suppressing the decay of magnetization in recorded
magnetization caused by reproducing output fluctuation and stray
magnetic fields to improve the surface flatness of the soft
magnetic underlayer and realize excellent fly ability of the
recording head and a high medium S/N ratio at 7.75 gigabits per
square centimeter. It is another feature of the present invention
to provide a highly reliable high density magnetic
recording/reproducing apparatus that uses the medium.
[0010] In one aspect, the perpendicular magnetic recording medium
of the present invention is structured so that a perpendicular
recording layer is formed over a substrate with a soft magnetic
underlayer therebetween and an amorphous layer or nano-crystalline
layer is formed between the substrate and the soft magnetic
underlayer while the soft magnetic underlayer includes first and
second amorphous soft magnetic layers and a nonmagnetic layer
formed between the first and second amorphous soft magnetic layers.
The first and second amorphous soft magnetic layers arc given
uniaxial anisotropy respectively and coupled with each other
antiferromagnetically. The magnetic recording/reproducing apparatus
of the present invention uses the perpendicular magnetic recording
medium.
[0011] In the above medium, the magnetization of the soft magnetic
underlayer is controlled and the underlayer is formed on an
amorphous layer or nano-crystalline layer, thereby suppressing the
decay of magnetization in recorded magnetization to be caused by
the output signal fluctuation and the stray field so as to improve
the fly ability of the recording head.
[0012] The method for manufacturing the perpendicular magnetic
recording medium according to one embodiment of the present
invention comprises forming an amorphous layer or nano-crystalline
layer over a substrate, forming a first amorphous soft magnetic
layer on the amorphous layer or nano-crystalline layer, forming a
nonmagnetic layer on the first amorphous soft magnetic layer,
forming a second amorphous soft magnetic layer on a nonmagnetic
layer, and forming a perpendicular recording layer on the second
amorphous soft magnetic layer. The method may further comprise
cooling the substrate while applying a magnetic field to the
substrate in its radial direction after at least any of the step of
forming the first amorphous soft magnetic layer and the step of
forming the second amorphous soft magnetic layer. Cooling the
substrate can give uniaxial anisotropy surely in the radial
direction of the disk substrate.
[0013] According to the present invention, therefore, it is
possible to realize a perpendicular magnetic recording medium
capable of suppressing both spike noise and amplitude modulation of
output signals, as well as the decay of recorded magnetization to
be caused by stray fields, and realizing excellent fly ability of
the recording head. In addition, it is possible to realize a highly
reliable and stable magnetic recording/reproducing apparatus having
a low error rate at 7.75 gigabits or over per square
centimeter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a layer configuration of a perpendicular recording
medium in an embodiment of the present invention;
[0015] FIG. 2 is a schematic block diagram of a film depositing
apparatus for manufacturing a medium in an embodiment of the
present invention;
[0016] FIG. 3 is graphs for curves obtained by differentiating each
of a magnetic curve of a soft magnetic underlayer of the medium A
in an embodiment of the present invention and a magnetic curve
measured by applying a magnetic field in the radial direction of
the substrate (A) by the magnetic field;
[0017] FIG. 4 is a graph for denoting a curve obtained by
differentiating a magnetic curve measured by applying a magnetic
field in the radial direction of the soft magnetic underlayer of
the medium V in a comparative example by the magnetic field;
[0018] FIG. 5 is a graph for denoting a curve obtained by
differentiating a magnetic curve measured by applying a magnetic
field in the radial direction of the soft magnetic underlayer of
the medium W in a comparative example by the magnetic field;
[0019] FIG. 6 is explanatory views of the magnetization of the
magnetic underlayers of the medium A in an embodiment of the
present invention and the medium W in a comparative example;
[0020] FIG. 7 illustrates how the spike noise is distributed in the
medium A in an embodiment of the present invention, as well as in
the medium V in a comparative example;
[0021] FIG. 8 is an explanatory view of a method for evaluating the
stray field resistance;
[0022] FIG. 9 is a graph for describing a relationship between an
external magnetic field and a standardized read output;
[0023] FIG. 10 is a timing of each cooling process for cooling the
soft magnetic underlayer;
[0024] FIG. 11 is a relationship between,the medium in an
embodiment of the present invention and the anti ferromagnetic
coupling magnetic field Hex value;
[0025] FIG. 12 is a magnetic domain structure of the medium A in an
embodiment of the present invention, as well as that of the second
amorphous soft magnetic layer of each of the media G and H in
comparative examples;
[0026] FIG. 13 is another layer configuration of the perpendicular
recording medium in an embodiment of the present invention;
[0027] FIG. 14 is a schematic block of a film depositing apparatus
for manufacturing the medium in an embodiment of the present
invention;
[0028] FIG. 15 is a graph for denoting how the antiferromagnetic
coupling magnetic field Hex temperature changes;
[0029] FIG. 16 illustrates the surface of the medium K in an
embodiment of the present invention, as well as those of the media
X and Y in examples for comparison after the corrosion resistance
evaluation;
[0030] FIG. 17 is a graph for describing the fly ability of the
medium in an embodiment of the present invention;
[0031] FIG. 18(a) is an explanatory top view of the magnetic
recording/reproducing apparatus in an embodiment of the present
invention and FIG. 18(b) is its cross sectional view of the
apparatus at the A-A' vertical line;
[0032] FIG. 19 is a graph for describing a relationship between the
FeCoB film thickness and the distortion of the glass substrate;
and
[0033] FIG. 20 is a magnetic domain structure of a soft magnetic
layer.
DETAILED DESCRIPTION OF THE INVENTION
[0034] Hereunder, the perpendicular magnetic recording medium of
the present invention will be described in detail with reference to
the accompanying drawings.
[0035] The perpendicular magnetic recording medium according to
embodiments of the present invention is structured so that an
amorphous layer or nano-crystalline layer is formed over the
substrate, a soft magnetic underlayer is formed on the amorphous
layer or nano-crystalline layer, and a perpendicular recording
layer is formed on the soft magnetic underlayer. This soft magnetic
underlayer includes first and second amorphous soft magnetic layers
and a nonmagnetic layer formed between the first and second
amorphous soft magnetic layers. The first and second amorphous soft
magnetic layers are given uniaxial anisotropy in the radial
direction of the disk substrate respectively and coupled with each
other anti ferromagnetically.
[0036] Then, a magnetic field is applied to the substrate of the
perpendicular magnetic recording medium in its radial direction to
measure the magnetization curve of the soft magnetic underlayer and
the magnetization curve is found to have a step-like shape having a
magnetization level stable within a magnetic field that includes
the zero field. The absolute value of the switching field of which
state is switched from negative field side saturation magnetization
to the stable magnetization level is almost the same as the
absolute value of the switching field of which state is switched
from positive field side saturation magnetization to the stable
magnetic level.
[0037] Furthermore, in the magnetization curve of the soft magnetic
underlayer measured by applying a magnetic field in the radial
direction of the substrate of the perpendicular magnetic recording
medium, the differential value of the magnetization curve of the
soft magnetic layer assumed when the state of the applied magnetic
field is changed from saturation magnetization to its reversed
saturation magnetization comes to have two peaks. The two peaks are
almost symmetrical about the zero field. The peak of the
differential value of the magnetization curve assumed when the
state of the applied magnetic field is changed from positive or
negative saturation magnetization to zero comes to almost lie upon
the peak of the differential value of the magnetization curve
assumed when the state of the applied magnetic field is changed
from zero to positive or negative saturation magnetization.
[0038] Each of the first and second amorphous soft magnetic layers
may be formed with any material if the material is given uniaxial
anisotropy in the radial direction of the substrate when the value
of Bs becomes at least over 1 Tesla, satisfies the coercivity
measured in the head running direction, which is under 1.6 kA/m,
and is excellent in surface flatness properties.
[0039] Concretely, the medium will have the above characteristics
easily if the medium is made of an amorphous alloy containing
mainly Co or Fe and such additives as Ta, Hf, Nb, Zr, Si, B, C,
etc. The film thickness should be over about 20 nm so that the
coercivity is controlled low. If the film thickness is under about
150 nm, the medium will be able to suppress spike noise and improve
the stray field robustness.
[0040] The magnetic moment should be equal between the first and
second amorphous soft magnetic layers so that a magnetic flux flows
between those layers, whereby the magnetic domains in the layers
are more stabilized.
[0041] The amorphous layer or nano-crystalline layer may be formed
with any material if the material is excellent in surface flatness
properties. However, the layer should preferably be formed with an
alloy containing at least two or more types of Ni, Al, Ti, Ta, Cr,
Zr, Co, Hf, Si, and B metal elements. More concretely, the layer
may be formed with NiTa, AlTi, AlTa, CrTi, CoTi, NiTaZr, NiCrZr,
CrTiAl, or the like. Using any of those materials will improve both
stress relaxation, scratch resistance, and corrosion
resistance.
[0042] The amorphous layer or nano-crystalline layer should
preferably be about 1 nm to 100 nm in thickness. If the amorphous
layer or nano-crystalline layer is under about 1 nm in thickness,
it might not compensate the surface roughness of the disk
substrate. If the amorphous layer or nano-crystalline layer is over
about 100 nm in thickness, the substrate temperature might rise
when in film deposition, whereby the first amorphous soft magnetic
layer to be formed on the amorphous layer or nano-crystalline layer
might be crystallized, and the medium characteristics are
lowered.
[0043] As described above, the perpendicular magnetic recording
medium according to embodiments of the present invention can
promote the stress relaxation of the amorphous soft magnetic layer
and reduce the distortion of the substrate, so that the medium
comes to have excellent fly ability. Although the first and second
amorphous soft magnetic layers come to have a multi-magnetic domain
structure respectively, both spike noise and output signal
amplitude modulation are suppressed, whereby the reliability of the
medium is further improved.
[0044] FIG. 19 shows a result of comparison of the substrate
distortion between when an amorphous soft magnetic layer (FeCoB) is
formed directly on the glass substrate and when the amorphous soft
magnetic layer (FeCoB) is formed over the glass substrate with an
amorphous layer (NiTaZr) therebetween at a thickness of 50 to 200
nm respectively.
[0045] It would be understood from FIG. 19 that the substrate
distortion increases in proportion to an increase of the thickness
of the FeCoB layer. If the FeCoB layer is formed over the glass
substrate with an amorphous layer therebetween, the substrate
distortion is reduced to a half of that when the FeCoB layer is
formed directly on the glass substrate.
[0046] FIG. 20 shows a result of observation of the magnetic domain
structure of the FeCoB layer through an optical surface analyzer
when the FeCoB layer is formed at a thickness of 200 nm.
[0047] If the FeCoB layer is formed directly on the glass
substrate, the domain image appears as shown in FIG. 20(a). On the
other hand, if the FeCoB layer is formed over the glass substrate
with an NiTaZr layer therebetween, the domain structure comes to
have a magnetic wall extended in the radial direction of the,
substrate as shown in FIG. 20(b).
[0048] Such a material as FeCoB having a large film stress causes
the coercivity to increase when it is deposited directly on the
substrate, so that the uniaxial anisotropy is reduced. If the
material is deposited on an NiTaZr layer, however, the film stress
is relaxed; whereby the layer is given uniaxial anisotropy in the
radial direction of the substrate regardless of the FeCoB film
thickness.
[0049] Consequently, because the amorphous soft magnetic layer is
formed over the glass substrate with an amorphous layer
therebetween, the film stress is relaxed and the soft magnetic
characteristic is improved clearly. The same effect is also
obtained if the amorphous soft magnetic layer is formed with a
material containing at least two types of Ni, Al, Ti, Ta, Cr, Zr,
Co, Hf, Si, and B metal elements, concretely with any of NiTa,
AlTi, AlTa, CrTi, CoTi, NiCrZr, CrTiAl, etc.
[0050] The amorphous layer formed between the first and second
amorphous soft magnetic layers functions to enable the first and
second amorphous soft magnetic layers to be coupled with each other
antiferromagnetically. Ru or Cu should preferably be used when an
amorphous alloy containing Co mainly is used to form the both soft
magnetic layers while Cr or Ru should preferably be used when an
amorphous alloy containing Fe mainly is used to form the both soft
magnetic layers.
[0051] The thickness of the nonmagnetic layer is just required to
be set so as to enable anti-ferromagnetic coupling between the both
soft magnetic layers. However, the optimal thickness depends on
various conditions such as the material of the both soft magnetic
layers, the depositing condition, and the substrate temperature
when in film deposition. For example, if an amorphous alloy
containing mainly Co is used to form the both soft magnetic layers
and Ru is used to form the nonmagnetic layer, the Ru layer should
preferably be set around 0.5 to 1.5 nm in thickness.
[0052] It is effective to take a sandwich structure in which the
nonmagnetic layer is put between thin ferromagnetic layers having a
thickness of about 1 to 5 nm respectively to make it stronger the
anti-ferromagnetic coupling between the first and second amorphous
soft magnetic layers. Concretely, for example, a laminated layer
consisting of three layers of Co/Ru/Co, CoFe/Ru/CoFe, Fe/Cr/Fe, or
the like may be used. An alloy of non-material and ferromagnetic
layers may also be used for the non-material layer to obtain the
same effect. Concretely, for example, RuCo, RuFe, or the like may
be used.
[0053] Furthermore, the disk substrate is cooled enough after the
first amorphous soft magnetic layer is formed so as to form the
nonmagnetic film, thereby enabling the antiferromagnetic coupling
between the soft magnetic layer and the nonmagnetic layer to
function more stably.
[0054] While the substrate is cooled, a magnetic field should
preferably be applied in the radial direction of the substrate. At
that time, the magnetization of the first amorphous soft magnetic
layer in the radial direction must be saturated and it is just
required to apply a magnetic field in the radial direction of the
disk substrate so that the magnetic field magnitude becomes 4 kA/m
and over. This cooling process carried out in the magnetic field
can give uniaxial anisotropy to the first amorphous soft magnetic
layer more surely.
[0055] The cooling temperature is lowered down to, for example,
about 100.degree. C., which is lower than the temperature in the
process of forming the first amorphous soft magnetic layer, then
preferably the temperature is lowered down to the room temperature.
This cooling process can thus make the antiferromagnetic coupling
between the soft magnetic layer and the nonmagnetic layer to
function stably.
[0056] In addition, the substrate cooling process may be provided
after the second amorphous soft magnetic layer deposition process.
In that connection, the process should be controlled so that the
substrate temperature is prevented from rising after the first
amorphous soft magnetic layer is formed.
[0057] Furthermore, the substrate cooling process may be provided
at two places after the first and second amorphous soft magnetic
layers deposition processes. In that connection, the uniaxial
anisotropy is given more surely to the first and second amorphous
soft magnetic layers respectively.
[0058] The substrate cooling should preferably be provided before
the nonmagnetic layer deposition process. This is because the
nonmagnetic layer is so thin and interfacial diffusion might occur
depending on the combination of materials, the film thickness, or
the depositing condition when in depositing of the nonmagnetic
layer, as well as because the interface between the first and
second amorphous soft magnetic layers is crystallized, whereby the
antiferromagnetic coupling might be disabled. Particularly, if the
disk temperature is very high before the amorphous layer is formed,
much care should be given to those points.
[0059] If the cooling process is provided after the deposition
processes of the first and second amorphous soft magnetic layers,
the nonmagnetic layer may be formed as a three-layer film of
Co/Ru/Co, or the like or as an alloy layer of RuCo, or the like.
Consequently, the interfacial diffusion of the nonmagnetic layer is
suppressed enough, whereby desired characteristics are
obtained.
[0060] Furthermore, an intermediate layer should preferably be
formed between the perpendicular recording layer and the soft
magnetic underlayer so that medium noise is suppressed. The
intermediate layer may be formed with an alloy structured as
amorphous or hexagonal closed packed structure or face-center cubic
structure. The intermediate layer may also be formed as a
single-layer film or laminated layer formed with different crystal
structure materials.
[0061] The perpendicular recording layer may be formed with such a
hcp-Co alloy film as a CoCrPt alloy, a CoCrPtB alloy, or the like,
such a granular film as a CoCrPt--SiO.sub.2 or the like, a
superlattice film such as a (Co/Pd) multilayer film, a (CoB/Pd)
multilayer film, a (CoSi/Pd) multilayer film, a Co/Pt multilayer
film, a (CoB/Pt) multilayer film, a (CoSifPt) multilayer film, or
the like.
[0062] The protective layer of the perpendicular recording layer
should preferably be formed as a laminated layer consisting of a
film containing carbon mainly and having a thickness of about 2 nm
to 8 nm and such a lubricant layer as a perfluoro alkyl poly-ethere
or the like. As a result, the reliability of the perpendicular
magnetic recording medium is further improved.
[0063] The magnetic recording/reproducing apparatus according to an
embodiment of the present invention comprises a perpendicular
magnetic recording medium described above, a driving element for
driving the medium in the recording direction, a magnetic head
including a write element and a read element, a mechanism for
moving the magnetic head relatively with respect to the
perpendicular magnetic recording medium, and a write/read channel
for writing/reading signals to/from the magnetic head. The read
element of the magnetic head is composed of a single pole type head
and the read element of the magnetic head is composed of a high
sensitive element that employs magnetoresistance or tunneling
magneto-resistance. Consequently, the present invention comes to
realize a highly reliable magnetic recording/reproducing apparatus
having areal recording density as high as 7.75 gigabits per square
centimeter.
[0064] Hereinafter, the embodiments of the present invention will
be described in detail with reference to the accompanying
drawings.
First Embodiment
[0065] FIG. 1 shows a structure of a perpendicular magnetic
recording medium in this first embodiment. On a 2.5-inch glass disk
substrate 11 were formed an amorphous layer 12, a first amorphous
soft magnetic layer 13, a nonmagnetic layer 14, a second amorphous
soft magnetic layer 15, an intermediate layer 16, a perpendicular
recording layer 17, and a protective layer 18 successively with use
of a sputtering method. Table 1 shows the target, the Ar gas
pressure, and the film thickness of each layer of the medium.
TABLE-US-00001 TABLE 1 Ar gas Film Target pressure thickness
composition (Pa) (nm) Amorphous layer 12
Ni.sub.52.5Ta.sub.37.5Zr.sub.10 1 30 First amorphous soft
Co.sub.92Ta.sub.3Zr.sub.5 0.5 50-100 magnetic layer 13
Fe.sub.57Co.sub.31B.sub.12 0.5 100 Nonmagnetic layer 14 Ru 0.6 0.8
Second amorphous soft Co.sub.92Ta.sub.3Zr.sub.5 0.5 50-100 magnetic
layer 15 Fe.sub.57Co.sub.31B.sub.12 0.5 100 Intermediate layer 16
Ru 2 20 Perpendicular recording CoCr.sub.13Pt.sub.14--SiO.sub.2 2
20 layer 17 Protective layer 18 Carbon 1 5
[0066] At first, NiTaZr to form the amorphous layer 12 and CoTaZr
or FeCoB to form the first amorphous soft magnetic layer 13 were
deposited on the substrate 11 successively. After that, the
substrate 11 was cooled down to about 80.degree. C. in the magnetic
field with use of helium gas to deposit Ru to form the nonmagnetic
layer 14 and CoTaZr or FeCoB to form the second amorphous soft
magnetic layer 15. The substrate 11 was then cooled down to
80.degree. C. with use of the helium gas to deposit Ru to form the
intermediate layer 16 and CoCrPt--SiO.sub.2 to form the recording
layer 17 successively. After that, carbon was deposited to form the
protective layer 18. The magnitude of magnetic field in the cooling
process was 4 kA/m. After that, lubricant consisting of perfluoro
alkyl poly-ethere thinned with perfluoro alkyl poly-ether was
coated. Thus, the perpendicular magnetic recording medium in this
first embodiment was completed.
[0067] FIG. 2 shows a schematic block diagram of a film depositing
apparatus for manufacturing the medium in the first embodiment. The
depositing apparatus comprises a substrate load chamber, an
amorphous layer deposition chamber, a first amorphous soft magnetic
layer deposition chamber, a first substrate cooling chamber while
applying a magnetic field in the radial direction of the substrate,
a nonmagnetic layer deposition chamber, a second amorphous soft
magnetic layer deposition chamber, a second substrate cooling
chamber while applying a magnetic field in the radial direction of
the substrate, an intermediate layer deposition chamber, and a
recording layer deposition chamber, a protective layer deposition
chamber, and a substrate unload chamber.
[0068] Two media V and W are prepared for comparison. In the medium
V, NiTaZr is deposited to form the amorphous layer between the
first and second amorphous soft magnetic layers. In the medium W,
FeAlSi is deposited to form the soft magnetic layer. Other layers
are formed in the same way as those of the medium in this first
embodiment.
[0069] FIG. 3(a) shows a magnetization curve of the soft magnetic
underlayer in this first embodiment, which was measured by a
vibrating sample magnetometer (VSM).
[0070] The magnetization curve measured by applying a magnetic
field in the radial direction of the substrate in this first
embodiment has a step-like shape having a magnetization level (the
first and second amorphous soft magnetic layers are magnetized in
anti-parallel to each other: II) stable within a magnetic field
range that includes the zero field. In addition, the absolute value
of the switching field of which state is switched from negative
field saturation magnetization (I) to the stable magnetization
level is almost the same as the absolute value of the switching
field of which level is switched from the positive field saturation
level (III) to the stable magnetization level.
[0071] The magnetization curve measured by applying a magnetic
field in the radial direction of the substrate denotes that both
magnetic field and magnetizing direction change almost
linearly.
[0072] FIG. 3(b) shows a result of differentiation of the
magnetization curve (a) measured by applying a magnetic field in
the radial direction of the substrate with respect to the magnetic
field. This differential value has four peaks that appear when the
applied magnetic field changes from positive to negative and from
negative to positive. The two peaks recognized when the applied
magnetic field is changed from positive saturation magnetization
level to zero and from zero to the positive saturation
magnetization level almost lie one upon another and those two peaks
and other two peaks recognized when the applied magnetization level
is changed from the negative saturation magnetization to zero and
from zero to the negative saturation magnetization are almost
symmetrical about the magnetic field zero.
[0073] In a soft magnetic underlayer having a differential curve as
shown in FIG. 3(b), the first and second amorphous soft magnetic
layers are given uniaxial anisotropy respectively in the radial
direction of the substrate and coupled with each other
antiferromagnctically just as in this embodiment.
[0074] The center value of the absolute values of the two peaks
recognized at the positive field side denotes a switching field (in
which the magnetization level is switched and hereinafter, to be
referred to as antiferromagnetic coupling magnetic field Hex) shown
in FIG. 3(a).
[0075] In the range in which these two peaks appear, the first and
second amorphous soft magnetic layers are coupled with each other
antiferromagnetically, so that their magnetization state can be
suppressed from change's to be caused by external magnetic
fields.
[0076] FIG. 4 shows a curve obtained by differentiating a
magnetization curve of the medium V in a comparative example with
respect to the magnetic field; and FIG. 5 shows a curve obtained by
differentiating a magnetization curve of the medium W in a
comparative example, measured by applying a magnetic field in the
radial direction of the substrate with respect to the magnetic
field.
[0077] Unlike the differential value in FIG. 3(b), the differential
value in FIG. 4 enables one peak to be recognized around the zero
field when the applied magnetic field level is changed from
positive saturation magnetization to negative one. In a soft
magnetic underlayer having such a curve, the first and second
amorphous soft magnetic layers are not coupled with each other
antiferromagnetically while they are given uniaxial anisotropy
respectively. Their magnetization states thus come to be changed
easily in response to a small external magnetic field.
[0078] Similarly to the medium in this first embodiment, the
differential value shown in FIG. 5 has four peaks. The two peaks
recognized at the positive or negative magnetic field side do not
lie one upon another and they are not symmetrical about the field
zero. In a soft magnetic underlayer having such a curve, the first
and second amorphous soft magnetic layers are magnetized at random,
that is, not in parallel to each other in the radial direction of
the substrate while they are coupled with each other
antiferromagnetically. In other words, each of the first and second
amorphous soft magnetic layers is given no uniaxial anisotropy in
the radial direction of the substrate. When compared with the
medium A in this first embodiment, therefore, the medium comes to
have a small Hex value and weak in stray field robustness.
[0079] FIG. 6 shows an explanatory view of the state of the
remanence of the second amorphous soft magnetic layer to be
expected from the differential curve shown in FIG. 3 or 5.
[0080] The first amorphous soft magnetic layer 13 of the medium A
in this embodiment is magnetized almost in parallel to the radial
direction of the substrate and the second amorphous soft magnetic
layer 15 is magnetized in anti-parallel to the first amorphous soft
magnetic layer 13. However, because the first and second amorphous
soft magnetic layers are not magnetized in one direction such way,
the layers are considered to have a multi-domain structure
respectively.
[0081] In the medium W in the comparative example, the first and
second amorphous soft magnetic layers are magnetized in
anti-parallel to each other, that is, magnetized at random. When
compared with the medium A in this first embodiment, therefore, the
medium is considered to have a more minute magnetic domain
structure.
[0082] FIG. 7 shows spike noise maps of the medium A in this first
embodiment and the medium V in the comparative example. In FIG. 7,
a spin stand and a digital oscilloscope were used to evaluate a
disk radius range of 16 to 30 mm at 100 .mu.m pitches. In the
medium V in the comparative example, two types of spike noise were
observed; large spike noise possibly caused by the magnetic domain
wall and spot-like distributed spike noise. In the medium A in this
first embodiment, however, no distinct spike noise was
recognized.
[0083] Although each of the first and second amorphous soft
magnetic layers 13 and 15 has a multi-domain structure in the soft
magnetic layer in this first embodiment as described above, the
closure flux flows through those layers. Thus, the underlayer was
found to be effective to suppress spike noise significantly.
[0084] Next, a description will be made for results of evaluation
of the spike noise of the medium and the amplitude modulation of
read signals examined in this first embodiment and tabulated in
Table 2.
TABLE-US-00002 TABLE 2 Constitution of soft magnetic underlayer,
parenthesized number means film thickness Hex Amplitude Medium
(unit: nm) (Oe) Spike noise modulation This A
CoTaZr(100)/Ru(0.8)/CoTaZr(100) 23 Absent Not made embodiment B
CoTaZr(75)/Ru(0.8)/CoTaZr(75) 33 Absent Not made C
CoTaZr(50)/Ru(0.8)/CoTaZr(50) 45 Absent Not made D
FeCoB(75)/Ru(0.8)/FeCoB(75) 43 Absent Not made Comparative V
CoTaZr(100)/NiTaZr(5)/CoTaZr(100) 0 Present Made example W
FeSiAl(100)/Cr(1)/FeSiAl(100) 15 Absent Made
[0085] In any of the media A to D in this embodiment and the medium
W in the comparative example, no distinct spike noise was observed.
This is because the first and second amorphous soft magnetic layers
were coupled with each other anti ferromagnetically, whereby those
layers were magnetized in anti-parallel to each other. In the media
V and W, however, read signal amplitude modulation was
observed.
[0086] Next, a description will be made for results of evaluation
of the stray field resistance of the media A, V, and W. As shown in
FIG. 8, a coil was disposed on each of the media and a current was
flown in the coil to apply a magnetic field to the medium so as to
check how reproducing output signals change in level with respect
to the external magnetic field.
[0087] FIG. 9 shows results of the evaluation. The external
magnetic field of which output was lowered by 10% was as follows;
1.0 kA/m for the medium V (comparative example) and 2.2 kA/m for
the medium W in which the first and second amorphous soft magnetic
layers were coupled with each other antiferromagnetically. On the
other hand, the external magnetic field output was about 4.0 kA/m
for the medium A of the present invention. This proved that the
external magnetic field resistance was improved.
[0088] In this first embodiment, the amorphous layer was formed
with NiTaZr. However, it is already known that the same effect is
also obtained even when the amorphous layer is formed with a
material containing at least two or more types of Ni, Al, Ti, Ta,
Cr, Zr, Co, Hf, Si, and B metal elements, concretely with any of
NiTa, AlTi, AlTa, CrTi, CoTi, NiCrZr, CrTiAl, etc.
[0089] Because the first and second amorphous soft magnetic layers
were magnetized in anti-parallel to each other and the magnetic
moment was equal between those layers, whereby a magnetic flux flew
between those layers in the soft magnetic underlayer of the present
invention, the underlayer was found apparently to be effective
significantly to suppress both spike noise and read signal
amplitude modification. In addition, the underlayer was also found
to be effective to give uniaxial anisotropy to the first and second
amorphous soft magnetic layers in the radial direction of the
substrate respectively to reduce the coercivity, thereby improving
the stray magnetic field resistance.
Second Embodiment
[0090] In this second embodiment, a description will be made for a
result of checking a relationship between the cooling timing and
the antiferromagnetic coupling magnetic field magnitude Hex that
works between the first and second amorphous soft magnetic layers
using a medium manufactured just as the medium A in the first
embodiment.
[0091] FIG. 10 shows a schematic block diagram of deposition
processes for manufacturing the media used in this second
embodiment and comparative examples.
[0092] The deposition process (1) is a process for manufacturing
the medium A used in this second embodiment. A cooling process is
provided between a process for forming the first amorphous soft
magnetic layer 14 and a process for forming the nonmagnetic layer
14.
[0093] The deposition process (2) for manufacturing the medium in
the comparative example includes a cooling process provided between
the process for forming the nonmagnetic layer 14 and the process
for forming the second amorphous soft magnetic layer 15.
[0094] The deposition process (3) includes a cooling process
provided between the process for forming the second amorphous soft
magnetic layer 15 and the process for forming the intermediate
layer 16.
[0095] The cooling unit is composed of two copper-made cooling
plates and a coil for applying a magnetic field to each object disk
substrate. In this second embodiment, the temperature of the
cooling plates was lowered to -100.degree. C. or less and the
substrate was cooled in the magnetic field for five seconds in an
hydrogen or helium atmosphere at a pressure of about 200 Pa. In the
cooling process, the magnetic field was applied in the radial
direction of the disk substrate and the polarity of the magnetic
field was adjusted to the polarity of the leak magnetic field from
the DC magnetron sputtering cathode so that the magnetic field
magnitude became within 4 kA/m to 8 kA/m on the disk substrate.
[0096] Table 3 shows results of evaluation of both spike noise and
read signal amplitude modulation with respect to the media in this
second embodiment and the comparative examples, as well as the
average and variations of Hex values measured at 32 different
places. In any of the medium A in this second embodiment and the
media E and F in the comparative examples that were cooled in the
magnetic field respectively, no distinct spike noise was observed
regardless of the timing of the cooling process. However, in the
medium G in the comparative example that was cooled without
applying any magnetic field (in the nonmagnetic field) and the
medium H that was not cooled at all, a lot of spike noise was
observed and the read signal amplitude modulation was found to be
significant.
TABLE-US-00003 TABLE 3 Deposition Magnetic Spike Amplitude Hex
Longitudinal Medium process field Noise modulation (Oe) variation
This embodiment A (1) Present Absent Not made 23 17% Comparative E
(2) Present Absent Made 19.5 25% example F (3) Present Absent Made
15.2 100% G (3) Absent Present Made 4.8 >100% H None Absent
Present Made 2 >100%
[0097] FIG. 11 shows a relationship between each of the above media
and the ferromagnetic coupling magnetic field Hex that works
between the first and second amorphous soft magnetic layers. In
FIG. 11, variations found at the 32 different places of each medium
were also shown.
[0098] The medium A in this second embodiment obtained the maximum
Hex value and the Hex value was found to be distributed less
throughout the disk, that was only about 17%. On the other hand, in
the media E and F that were cooled in the magnetic field, the Hex
value was smaller than that of the medium A and the positional
distribution was large. The most effective method found for
obtaining a large Hex value for a medium was to cool the medium in
the magnetic field after the first amorphous soft magnetic layer
was formed.
[0099] The medium G cooled while no magnetic field was applied
thereon in the deposition process (3) obtained almost the same Hex
value as that of the medium F cooled in the magnetic field in the
deposition process (3). However, the Hex value of the medium G was
varied significantly within 0 to 190, so that the antiferromagnetic
coupling between the layers was found to be lost partially.
[0100] On the other hand, the first and second amorphous soft
magnetic layers were found to be strongly exchange-coupled with
each other in the medium H that was not cooled at all.
[0101] FIG. 12 shows a result of observation of the magnetic domain
structures of the second amorphous soft magnetic layers of the
media A, G, and H with use of an optical surface analyzer. The
intermediate layer 16 and the perpendicular layer 17 were not
formed in any of the samples used here.
[0102] In the medium A in this embodiment, the magnetic domain of
the second amorphous soft magnetic layer was found to include
regions with different contrasts. Thus, the magnetic domain came to
have a multi-domain structure. The magnetic domain was
comparatively large and stable in state.
[0103] On the other hand, in each of the media G and H, the
magnetic domain image had a magnetic domain wall extended in the
radial direction of the substrate as seen in a single layer film.
It was also found from the magnetic domain structure that the
antiferromagnetic coupling between the first and second amorphous
soft magnetic layers was lost partially.
[0104] As described above, the soft magnetic underlayer formed
according to the manufacturing method of the present invention was
apparently effective to suppress both spike noise and amplitude
modulation of read signals, since the magnetic field of the
antiferromagnetic coupling that worked between the first and second
amorphous soft magnetic layers was large and the positional
distribution of the magnetic field was not so large.
Third Embodiment
[0105] FIG. 13 shows a layer configuration of a perpendicular
magnetic recording medium in this third embodiment. On a 2.5 type
glass substrate 130 were formed an amorphous layer 131, a first
amorphous soft magnetic layer 132, a first ferromagnetic layer 133,
a nonmagnetic layer 134, a second ferromagnetic layer 135, and a
second amorphous soft magnetic layer 136 successively with use of
the sputtering method. The medium was then cooled down to about
100.degree. C. in the magnetic field. After that, an intermediate
layer 137, a perpendicular recording layer 138, and a protective
layer 139 were formed successively on the substrate 130.
[0106] While the medium was cooled, the magnetic field was oriented
from outer periphery to inner periphery in the radial direction of
the disk substrate and the magnetic field magnitude was controlled
within 4 kA/m to 8 kA/m on the disk substrate.
[0107] Table 4 shows both Ar gas pressure and film thickness of
each target used for forming each layer of the medium in this third
embodiment. A coat of a lubricant obtained by thinning a per fluoro
alkyl poly-ethere material by a fluoro carbon material was applied
on the lubricant layer.
[0108] FIG. 14 shows a schematic sequence of processes of a
depositing apparatus for manufacturing the medium in this third
embodiment. The depositing apparatus in this third embodiment
comprises a substrate load chamber, an amorphous layer deposition
chamber, a first amorphous soft magnetic layer deposition chamber,
a ferromagnetic layer deposition chamber, a nonmagnetic layer
deposition chamber, a second amorphous soft magnetic layer
deposition chamber, a substrate cooling chamber for cooling each
substrate while applying a magnetic field in the radial direction
of the substrate, an intermediate layer deposition chamber, a
recording layer deposition chamber, a protective layer deposition
chamber, and a substrate unload chamber.
[0109] The cooling timing in this third embodiment provided between
the second amorphous soft magnetic layer 136 deposition process and
the nonmagnetic layer 137 deposition process is identical to the
deposition process (3) shown in FIG. 10 in the second
embodiment.
TABLE-US-00004 TABLE 4 Target Ar gas Film composition pressure (Pa)
thickness (nm) Amorphous layer 131 CrTi.sub.50 1 20 First amorphous
soft Fe.sub.57Co.sub.31B.sub.12 0.5 75 magnetic layer 132
Ferromagnetic layers Co.sub.90Fe.sub.10 1 2 133, 135 Nonmagnetic
layer 134 Ru 0.6 0.8 Ru.sub.70Fe.sub.30 0.6 1 Second amorphous soft
Fe.sub.57Co.sub.31B.sub.12 0.5 75 magnetic layer 136 Intermediate
layer 137 Ta/Ru 2 1/18 Recording layer 138
CoCr.sub.13Pt.sub.17--SiO.sub.2 2 16 Protective layer 139 Carbon 1
5
[0110] The magnetic curve of the soft magnetic underlayer in this
embodiment denotes a step-like shape having a stable magnetization
level within the magnetic field including the zero field just as in
the first embodiment if a magnetic field is applied in the radial
direction of the disk substrate.
[0111] Table 5 shows results of the evaluation of the media I and J
examined in this third embodiment, the strength of the
antiferromagnetic coupling magnetic field that functions between
the first and second amorphous soft magnetic layers of the medium D
examined in the first embodiment, as well as the evaluation of both
spike noise and amplitude modulation of read signals.
[0112] The Hex value of the ferromagnetic coupling magnetic field
of each of the media I and J as shown in Table 5 denotes a value
equivalent to that of the medium D in the first embodiment. When
the Hex values of the media A and F of the second embodiment are
compared with each other, the Hex value is reduced from 23 Oe to 15
Oe when the cooling timing in the cooling process is changed from
(1) to (3) in FIG. 10.
[0113] In each of the media I and J in this third embodiment, the
Hex value was not reduced even when the cooling timing in the
cooling process was set after the second amorphous soft magnetic
layer was formed just as in (3) in FIG. 10. This means that the
CoFe/Ru/CoFe three-layer film or RuFe layer is formed stably
between the first and second amorphous soft magnetic layers. In
other words, the medium in this third embodiment is improved for
the thermal resistance at the interface between the nonmagnetic
layer and the ferromagnetic layer or at the interface between the
amorphous soft magnetic layer and the nonmagnetic layer.
TABLE-US-00005 TABLE 5 Constitution of soft magnetic underlayer,
parenthesized number means film thickness Hex Amplitude Medium
(unit: nm) (Oe) Spike noise modulation This D
FeCoB(75)/Ru(0.8)/FeCoB(75) 43 Absent Not made embodiment I
FeCoB(75)/CoFe(2)/Ru(0.8)/CoFe(2)/FeCoB(75) 45 Absent Not made J
FeCoB(75)/RuFe(1)/FeCoB(75) 48 Absent Not made
[0114] FIG. 15 shows results of the evaluation of the thermal
resistance of each of the media I and J in this third embodiment,
as well as the medium D in the first embodiment.
[0115] Hex values are normalized by the value at as-deposited. The
Hex value decreases in proportion to an increase of the
environmental temperature. At 250.degree. C., the falling rate of
the Hex value is 0.62 for the medium D, 0.82 for the medium I in
which a CoFe/Ru/CoFe three-layer film is provided between the first
and second amorphous soft magnetic layers, and about 0.79 for the
medium J in which the Ru layer is replaced with a RuFe layer. The
thermal resistance of the media I and J is apparently improved more
than that of the medium D.
[0116] In this third embodiment, the cooling process was provided
between the second amorphous soft magnetic layer deposition process
and the intermediate layer deposition process. However, the cooling
process may also be provided between the intermediate layer
deposition process and the recording layer deposition process if
the intermediate layer is to be deposited at a high temperature and
the recording layer is deposited at a low temperature. If a heating
process is required after the recording layer deposition, the
cooling process may be provided between the recording layer heating
process and the protective layer deposition process.
[0117] The method for manufacturing the perpendicular recording
medium of the present invention can set a cooling process timing
after depositing the second amorphous soft magnetic layer or
perpendicular recording layer in the medium manufacturing process.
Particularly, the manufacturing cost of the perpendicular recording
medium can be reduced if a high deposition temperature of the
intermediate layer or perpendicular recording layer is
required.
Fourth Embodiment
[0118] In this fourth embodiment, evaluation was made for both
spike noise and amplitude modulation of read signals using a medium
B described in the first embodiment, a medium K that used NiCrZr
for the amorphous layer and a medium L that used AlTi for the
amorphous layer while they were configured just as the medium B, as
well as a medium X in which the first amorphous soft magnetic layer
was formed directly on the substrate as a comparative example, and
a medium Y in which the first amorphous soft magnetic layer was
formed on a crystalline NiCr layer. Table 6 shows the evaluation
results. While read signal amplitude modulation was recognized in
the medium X in which the soft magnetic underlayer was formed
directly on the substrate, the spike noise was suppressed in each
of the evaluated media.
TABLE-US-00006 TABLE 6 Constitution of soft magnetic underlayer,
parenthesized Amplitude Medium number means film thickness (unit:
nm) Spike noise modulation This B NiTaZr(30)
CoTaZr(75)/Ru(0.8)/CoTaZr(75) Absent Not made embodiment K
NiCrZr(30) CoTaZr(75)/Ru(0.8)/CoTaZr(75) Absent Not made L AlTi(30)
CoTaZr(75)/Ru(0.8)/CoTaZr(75) Absent Not made Comparative X --
CoTaZr(75)/Ru(0.8)/CoTaZr(75) Absent Made example Y NiCr(30)
CoTaZr(75)/Ru(0.8)/CoTaZr(75) Absent Not made
[0119] After that, a corrosion resistance test was performed for
the medium K in this embodiment, as well as for the media X and Y
in the comparative examples. The test conditions were set as
follows; the humidity was 100%, the temperature was 60.degree. C.,
and the test period was one week.
[0120] FIG. 16 shows images of the substrate surfaces of the tested
media observed with use of an optical surface analyzer. Each white
region denotes corrosion on the medium surface. In the case of the
medium X in which the soft magnetic layer is formed directly on the
substrate, corrosion was recognized throughout the disk surface. On
the contrary, the corrosion resistance was improved for the medium
for which a crystallized layer or amorphous layer was formed
between the substrate and the soft magnetic underlayer. The medium
B in which the soft magnetic underlayer was formed on an amorphous
layer was found to have the highest corrosion resistance. The same
effect as that of the medium K was also recognized in the medium B
or medium L in this embodiment.
[0121] After that, information was written/read in/from each of the
above media. A single pole head having a track width of 0.25 .mu.m
was used for writing and a GMR head having a shield gap of 0.08
.mu.m and a track width 0.22 .mu.m was used for reading.
[0122] Then, an error rate evaluation was made for the signal read
back waveform through an EEPR4 type signal processing circuit and
an error rate of about 10.sup.-6 was obtained from each of the
media B, K, and L and an error rate of about 10.sup.-5 were
obtained from each of the media X and Y under the areal recording
density of 7.75 gigabits per square centimeter. As a result, it was
found that the error rate for the medium in this embodiment in
which the soft magnetic underlayer was formed on an amorphous layer
was lower by a single digit than that of each of other media.
[0123] As is well known, the record/write separation type head is
configured by a main pole, a recording coil, an auxiliary
pole/upper shield, a GMR element, and a lower shield.
[0124] Four pieces were manufactured for each of the above media
and evaluated for the fly ability. FIG. 17 shows the results of the
evaluation. It was confirmed that each medium fly ability was
improved when the soft magnetic underlayer was formed on an
amorphous layer.
[0125] Next, a description will be made for an embodiment of a
general magnetic recording/reproducing apparatus of the present
invention with reference to FIG. 18. This apparatus comprises a
perpendicular magnetic recording medium 181, a motor element 182
for rotating the medium, a magnetic head 183, and its driving means
184, and a write/read channel 185 provided for the magnetic head
183. The magnetic head 183 is a write/read separation type one
provided on a magnetic head slider. The track width of the single
pole type recording head is 0.22 .mu.m and the shield-to-shield
separation of the magnetic head is 0.08 .mu.m, and the track width
is 0.22 .mu.m. Then, the medium A in the first embodiment was
loaded in the apparatus and the read/write characteristics were
evaluated at a head fly distance of 10 nm. At a temperature range
of 10.degree. C. and 50.degree. C., the performance of the medium
satisfied the read/write characteristic requirement of 7.75
gigabits per square centimeter.
Fifth Embodiment
[0126] The magnetic recording/reproducing apparatus in this fifth
embodiment was configured just as the apparatus in the fourth
embodiment. However, the apparatus in this fifth embodiment used a
high sensitivity element that made good use of the tunneling
magnetoresistance for the read head, then the medium A described in
the first embodiment was loaded in the apparatus for the
recording/reproducing evaluation at a head fly distance of 8 nm. As
a result of the evaluation, the 14-gigabit longitudinal recording
density read/write characteristics per square centimeter were
satisfied enough within a measurement range of 10.degree. C. to
50.degree. C. As is well known, the high sensitivity element that
used the magnetic tunneling effect used in this evaluation was
configured by an upper electrode, an antiferromagnetic layer, a
pinned layer, an insulating layer, a free layer, and a lower
electrode.
[0127] It is to be understood that the above description is
intended to be illustrative and not restrictive. Many embodiments
will be apparent to those of skill in the art upon reviewing the
above description. The scope of the invention should, therefore, be
determined not with reference to the above description, but instead
should be determined with reference to the appended claims alone
with their full scope of equivalents.
* * * * *