U.S. patent application number 10/965764 was filed with the patent office on 2005-05-19 for magnetic recording medium, the manufacturing method and magnetic recording apparatus using the same.
Invention is credited to Fujimaki, Shigehiko, Honda, Yoshinori, Kokaku, Yuuichi, Ono, Toshinori, Yatsue, Tooru.
Application Number | 20050106314 10/965764 |
Document ID | / |
Family ID | 18782225 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050106314 |
Kind Code |
A1 |
Ono, Toshinori ; et
al. |
May 19, 2005 |
Magnetic recording medium, the manufacturing method and magnetic
recording apparatus using the same
Abstract
This magnetic recording medium is characterized in that in the
magnetic recording medium having a magnetic film on a non-magnetic
substrate by intercalating at least an under layer, the proportion
of functional groups per 100 carbon atoms in a diamond-like carbon
protective coating mainly composed of carbon for protecting the
magnetic film exceeds 20%. The bonding force between the protective
coating layer and the lubricating layer of the magnetic recording
medium is increased so that under high speed rotation, a decrease
in the lubricating layer is not caused so as to provide a magnetic
recording apparatus having high reliability.
Inventors: |
Ono, Toshinori; (Odawara,
JP) ; Kokaku, Yuuichi; (Yokohama, JP) ; Honda,
Yoshinori; (Hiratsuka, JP) ; Fujimaki, Shigehiko;
(Machida, JP) ; Yatsue, Tooru; (Goleta,
CA) |
Correspondence
Address: |
KENYON & KENYON
1500 K STREET, N.W., SUITE 700
WASHINGTON
DC
20005
US
|
Family ID: |
18782225 |
Appl. No.: |
10/965764 |
Filed: |
October 18, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10965764 |
Oct 18, 2004 |
|
|
|
09784952 |
Feb 16, 2001 |
|
|
|
Current U.S.
Class: |
427/127 ;
427/249.7; 427/585; G9B/5.28; G9B/5.3 |
Current CPC
Class: |
G11B 5/72 20130101; G11B
5/8408 20130101 |
Class at
Publication: |
427/127 ;
427/249.7; 427/585 |
International
Class: |
B32B 001/00; C23C
016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2000 |
JP |
2000-300559 |
Claims
What is claimed is:
1. A manufacturing method for a magnetic recording medium, the
magnetic recording medium having a magnetic film on a non-magnetic
substrate formed by intercalating at least an under layer,
comprising forming a protective film mainly composed of carbon for
protecting the magnetic film by an ion beam method or a chemical
vapor deposition method, in which at least one gas among CO.sub.2,
NO.sub.2, N.sub.2O is added.
2. The manufacturing method for a magnetic recording medium
according to claim 1, wherein the protective coating is
diamond-like carbon.
3. The manufacturing method for a magnetic recording medium
according to claim 1, wherein when the protective coating is formed
by the ion beam method or the chemical vapor deposition method, at
least one of N.sub.2, Ne, Ar, Kr, Xe and hydrocarbon gas or
hydrocarbon gas is used.
4. A manufacturing method for a magnetic recording medium, the
magnetic recording medium having a magnetic film on a non-magnetic
substrate formed by intercalating at least an under layer,
comprising forming a diamond-like carbon protective coating mainly
composed of carbon for protecting the magnetic film by an ion beam
method or a chemical vapor deposition method, in which at least one
gas among CO.sub.2, NO.sub.2, N.sub.2O is added.
5. A manufacturing method for a magnetic recording medium, the
magnetic recording medium having a magnetic film, a protective
coating mainly composed of carbon for protecting the magnetic film
and a lubricating film of perfluoroether having at least one
functional group on a non-magnetic substrate, comprising forming
the protective coating by an ion beam method or a chemical vapor
deposition method using at least one of N.sub.2, Ne, Ar, Kr, Xe and
hydrocarbon gas or hydrocarbon gas, in which at least one gas among
CO.sub.2, NO.sub.2, and N.sub.2O is added.
6. A manufacturing method of a magnetic recording medium comprising
the steps of: forming an under layer on a non-magnetic substrate;
forming a magnetic film above said under layer; forming a
diamond-like carbon film above said magnetic film layer by a
chemical vapor deposition method in which N.sub.2O gas is
added.
7. The manufacturing method of a magnetic recording medium further
comprising the steps of: forming a lubricating film of
perfluoroether on said diamond-like film.
Description
[0001] This is a division of application Ser. No. 09/784,952 filed
16 Feb. 2001, the content of which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a magnetic recording medium which
has excellent reliability and in which magnetic recording is
performed with high density, a manufacturing method thereof and a
magnetic disc device used in an auxiliary storage apparatus of a
computer.
[0003] A magnetic disc apparatus used in a storage apparatus of a
large-scale computer, a work station, a personal computer and the
like has been yearly increased in its importance and developed into
a mass-stored and small sized device. Increasing of recording
density is essential to the development of the magnetic disc
apparatus into mass-stored and small-sized apparatus. As the
technology for realizing the development into the mass-stored and
small-sized device, cited is reduction in distance between a
magnetic recording layer of a magnetic recording medium and a
magnetic head.
[0004] The magnetic recording medium manufactured by sputtering has
been provided with a protective coating heretofore for the purpose
of protecting a magnetic film from sliding of a magnetic head.
Thinning of the protective coating and reduction of distance
between the surface of the protective coating and the magnetic head
are the most effective means for more decreasing the distance
between a magnetic recording layer and the magnetic head. For this
protective coating, carbon manufactured by DC sputtering, RF
sputtering (Japanese Patent Laid Open Hei 5-174369), or CVD
(Japanese Patent Laid-Open No. Hei 4-90125) is most generally used,
and a method of mixing nitrogen atoms, hydrogen atoms and the like
in the film to obtain a protective coating more excellent in
strength (Japanese Patent Laid-Open No. Sho 62-246129) has been
generally adopted. Further, it is general to use perfluoropolyether
liquid lubricant for the purpose of reducing friction between the
magnetic head and the magnetic recording medium.
[0005] As a general method for thinning, cited is to apply
diamond-like carbon (DLC) using ion beam deposition (IBD) or
chemical vapor deposition (CVD) for a protective coating. DLC,
however, bonding strength of carbon atoms and hydrogen atoms in the
thin film is generally strong and also its network has higher
continuity as compared with the carbon protective coating provided
by the sputtering. Therefore, the problem is that the bonding
strength to perfluoropolyether lubricant applied to the protective
coating is weak owing to fewer functional groups.
[0006] One of performance indexes of the magnetic recording device
using the magnetic recording medium is the data transfer rate. The
data transfer rate largely depends on the data access time. The
access time is composed of the seek time and the rotation waiting
time, and to shorten the rotation waiting time by increasing the
rotating speed of a magnetic recording medium leads to the
improvement in the data transfer rate.
[0007] When the rotating speed of the magnetic recording medium is
increased, however, centrifugal force is applied to the liquid
lubricant on the DLC protective coating of the magnetic recording
medium so that as the result of the problem that the bonding
strength is weak, the liquid lubricant is driven away toward the
outer peripheral part of the magnetic recording medium until it is
shaken off from the magnetic recording medium (hereinafter referred
to as spin-off). Consequently, the problem encountered is that the
lubricant on the magnetic recording medium is decreased to increase
the frictional force between the magnetic recording medium and the
magnetic head and cause a crash.
[0008] In order to solve the problems, attempts have been made to
apply surface treatment to the protective coating so as to increase
the bonding strength. Japanese Patent Laid-Open No. Sho 62-150526
and Japanese Patent Laid-Open No. Sho 63-2117 disclose that the
surface is subjected to plasma treatment. Japanese Patent Laid-Open
No. Hei 4-6624 discloses that the surface is subjected to
ultraviolet treatment, water treatment, ozonization or the like.
Further, Japanese Patent Laid-Open No. Sho 63-2117, Japanese Patent
Laid-Open No. Hei 9-30596, Japanese Patent Laid-Open No. Hei
8-225791, Japanese Patent Laid-Open No. Hei 7-210850 and Japanese
Patent Laid-Open No. Hei 5-174354 are similar to the above, and all
of these disclose that after the protective layer is formed, the
surface thereof is subjected to some treatment. These methods,
however, have the problem that it is difficult to uniformly treat
the whole surface, one additional process is needed in the work,
and besides the adhesion of the lubricant is insufficient.
SUMMARY OF THE INVENTION
[0009] The present invention has been made in view of the above
circumstances and provides a magnetic recording medium which is
increased in the chemical bonding strength of a protective coating
layer and liquid lubricant not to cause a decrease in liquid
lubricant due to spin-off under high speed rotation.
[0010] Further, the invention provides a manufacturing method for
the above magnetic recording medium.
[0011] Further, the invention provides a magnetic storage apparatus
suitable for reconciling high speed rotation and high reliability
by using the above magnetic recording medium.
[0012] To solve the above problems, the invention mainly adopts the
following constitution.
[0013] According to the invention, a magnetic recording medium is
characterized in that the magnetic recording medium has a magnetic
film formed on a non-magnetic substrate by intercalating at least
an under layer, and the proportion of functional groups per 100
carbon atoms in the diamond-like carbon protective coating mainly
composed of carbon, which protects the magnetic film, exceeds
20%.
[0014] In the case where a lubricating film of perfluoropolyether
having at least one functional group is provided on the protective
coating, bonding performance between the protective coating and the
lubricating film is excellent.
[0015] According to the invention, a manufacturing method for the
magnetic recording medium is characterized in that in the
manufacturing method for the magnetic recording medium having a
magnetic film formed on a non-magnetic substrate by intercalating
at least an under layer, when a protective coating mainly composed
of carbon for protecting the magnetic film is formed by an ion beam
method or a chemical vapor deposition method, at least one gas
among CO.sub.2, NO.sub.2, N.sub.2O is added.
[0016] In the case where the protective coating is diamond-like
carbon, the bonding performance between the protective coating and
the lubricating film is especially improved.
[0017] In the case of forming the protective coating by the ion
beam method or the chemical vapor deposition method, it is
preferable to use at least one of N.sub.2, Ne, Ar, Kr and Xe and
hydrocarbon gas or hydrocarbon gas.
[0018] In the manufacturing method for the magnetic recording
medium having a magnetic film formed on a non-magnetic substrate by
intercalating at least an under layer, at the time of forming a
diamond-like carbon protective coating mainly composed of carbon
for protecting the magnetic film by an ion beam method or a
chemical vapor deposition method, one gas among CO.sub.2, NO.sub.2,
N.sub.2O may be added.
[0019] According to the invention, a magnetic storage device is
characterized that the device includes the magnetic recording
medium, a driving part for driving the magnetic recording medium, a
magnetic head having a recording part and a reproducing part, a
recording reproducing signal processing part for giving and
receiving a signal to and from the magnetic head, and a
magnetoresistive head as a reproducing part of the magnetic
head.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Preferred embodiments of the present invention will be
described in detail based on the followings, wherein
[0021] FIG. 1 is a typical sectional view of a magnetic recording
medium according to the embodiment of the invention;
[0022] FIG. 2 is a schematic diagram of a protective coating
forming chamber 21;
[0023] FIG. 3 is a diagram showing the comparison of performance
between the magnetic recording media provided according to the
embodiment and the comparative example of the invention;
[0024] FIG. 4 is a diagram showing the general construction of a
magnetic storage device;
[0025] FIG. 5 is a typical perspective view of a magnetic head;
[0026] FIG. 6 is a diagram showing the sectional structure of a
magnetoresistive sensor; and
[0027] FIG. 7 is a sectional view of a sensor using a spin valve
head.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] First, the function, constitution and operation of the
invention will be described in brief in the following. In the
manufacturing method for the magnetic recording medium having a
magnetic film, a protective coating mainly composed of carbon for
protecting the magnetic film and a lubricating film of
perfluoropolyether having at least one functional group provided on
a substrate, at the time of forming the protective coating by an
ion beam method using at least one of N.sub.2, Ne, Ar, Kr, Xe and
hydrocarbon gas, or only the hydrocarbon gas or a CVD method, the
bonding performance between the protective coating and the
lubricating film is improved by adding at least one gas among
CO.sub.2, NO.sub.2, N.sub.2O.
[0029] In the magnetic recording medium provided by the above
method, the proportion of functional groups per 100 carbon atoms in
the protective coating can be over 20%.
[0030] The magnetic storage apparatus of the invention includes the
magnetic recording medium, a driving part for driving the magnetic
recording medium, a magnetic head formed by a recording part and a
reproducing part, a unit for moving the magnetic head relatively to
the magnetic recording medium, a signal input unit for inputting a
signal to the magnetic head and a recording reproducing signal
processing unit for reproducing an output signal from the magnetic
head, wherein the reproducing part of the magnetic head is formed
by a magnetoresistive head, and the magnetic recording medium is
formed by the magnetic recording medium including the protective
coating having the above characteristic quality, hardness and
thickness.
[0031] Further, the magnetoresistive sensor part of the
magnetoresistive head is formed between two shield layers which are
spaced from each other at a distance of 0.2 .mu.m or less and made
of soft magnetic substance, and the product Br.times.t of the
thickness (t) of the magnetic layer of the thus constructed
magnetic recording medium and the residual flux density Br measured
by applying a magnetic field in the relative traveling direction of
the magnetic head to the magnetic recording medium in recording
ranges from 3.2 mA (40 gauss micron) to 9.6 mA (120 gauss micron)
both inclusive.
[0032] The reason why the magnetoresistive sensor part of the
magnetoresistive head is to be formed between two shield layers
which are spaced from each other at a distance of 0.2 .mu.m or less
and made of soft magnetic substance is that in the magnetic storage
apparatus having the maximum track recording density of 220 kFCI,
sufficient reproducing output cannot be obtained. The distance
between two shield layers made of soft magnetic substance is
preferably 0.12 .mu.m or more in view of working easiness.
[0033] The reason why the product Br.times.t of the thickness (t)
of the magnetic layer of the thus constructed magnetic recording
medium and the residual flux density Br measured by applying a
magnetic field in the relative traveling direction of the magnetic
head to the magnetic recording medium in recording ranges from 3.2
mA (40 gauss micron) to 9.6 mA (120 gauss micron) both inclusive is
that when the Br.times.t is 3.2 mA (40 gauss micron), the risk of
reproducing wrong information becomes higher due to lowering of
reproducing output caused by being left for long time after
recording, and when it exceeds 9.6 mA (120 gauss micron), it
becomes difficult to overwrite in recording.
[0034] Further, by forming at least two layers of under layers in
the magnetic recording medium, the crystal orientation of the
magnetic layer may be controlled. By forming such multiple under
layer, the influence of atomic diffusion from the under layer to
the magnetic layer can be remarkably reduced, and simultaneously
the crystallinity of the under layer close to the magnetic layer
can be improved, and the adhesion between the magnetic layer and
the under layer becomes strong so as to obtain high sliding
resisting performance. Further, since the surface of the under
layer close to the magnetic layer has no atomic periodic array
extending over a long distance, the crystal grains of the magnetic
layer formed thereon may be refined and also the crystal
orientation may be controlled. Thus, the mean particle diameter of
crystal constituting the magnetic layer is controlled to 15 nm or
less suitable for reduction of noise, very fine size, and
simultaneously the direction of the axis of easy magnetization may
be controlled to be parallel to the film surface suitable for
in-plane magnetic recording.
[0035] The magnetoresistive head used in the magnetic storage
apparatus of the invention is formed by a magnetoresistive sensor
including plural conductive magnetic layers causing a large
resistance change due to a relative change of mutual magnetizing
directions by an external magnetic field, and a conductive
non-magnetic layer disposed between the conductive magnetic layers.
The reason why the thus constructed reproducing head is used is
that a signal recorded at the maximum track recording density
exceeding 300 kFCI is stably reproduced to obtain signal
output.
[0036] Further, the magnetoresistive head is formed on a magnetic
head slider, in which the area of the floating surface rail is
equal to or smaller than 1.00 mm.sup.2 and the mass is equal to or
less than 2 mg to achieve the invention. The reason why the area of
the floating surface rail is equal to or smaller than 1.00 mm.sup.2
is that the probability of colliding with the projection is
reduced, and simultaneously, the shock resistance reliability can
be improved by setting the mass equal to or less than 2 mg. Thus,
the recording density of 50 giga-bit per 1 in.sup.2 and high shock
resistance may be consistent with each other.
[0037] The embodiments of the invention will now be described in
detail. FIG. 1 shows one embodiment of the invention.
[0038] <Embodiment 1>
[0039] First, a soda lime glass substrate 1 (outside diameter of 84
mm, inside diameter of 25 mm and thickness of 1.1 mm) to be used is
sufficiently washed. This substrate is introduced into a vacuum
vessel evacuated to about 5.3.times.10E (-5)Pa (4.0.times.10E
(-7)Torr). First, it is transported to a first seed layer forming
chamber to form a first seed layer 2 of Ni-25 at. % Cr-15 at. % Zr
with a thickness of 20 nm under the condition of Ar atmosphere
about 0.8 Pa (6 mTorr) by the DC magnetron sputtering method.
Subsequently, it is transported to a second seed layer forming
chamber to form a second seed layer 3 of Co-40 at. % Cr-5 at. % Zr
with a thickness of 50 nm under the condition of Ar atmosphere
about 0.8 Pa (6 mTorr) by the DC magnetron sputtering method.
Subsequently, it is transported to a heating chamber in the vacuum
layer to heat the substrate to the substrate temperature
260.degree. C. by an infrared heater.
[0040] Subsequently, it is transported to an under layer forming
chamber to form an alloy under layer 4 of Cr-10 at. % Mo-7.5 at. %
Ti with a thickness of 30 nm under the condition of Ar atmosphere
about 0.8 Pa (6 mTorr) by the DC magnetron sputtering method.
Subsequently, it is transported to a magnetic recording layer
forming chamber to form an alloy layer 5 (to form a magnetic layer)
of Co-20 at. % Cr-4 at. % Ta-8 at. % Pt with a thickness of 22 nm
under the condition of Ar atmosphere about 0.9 Pa (7 mTorr) by DC
magnetron sputtering method. By using the substrate where the alloy
under layer 4 of Cr-10 at. % Mo-7.5 at. % Ti and the alloy layer 5
of Co-20 at. % Cr-4 at. % Ta-8 at. % Pt are formed, the protective
coating layer which is mentioned later and mainly composed of
carbon according to the invention is formed.
[0041] As the substrate 1, in addition to the soda lime glass, used
is a non-magnetic rigid substrate formed of chemical reinforced
aluminosilicate, an Al--Mg alloy electroless-plated with Ni--P,
silicon, ceramics made of borosilicate glass or the like, or
ceramics subjected to glass glazing or the like.
[0042] As the first and second seed layers are provided for
avoiding electrochemical precipitation of alkali metal from the
soda lime glass, they may have an arbitrary thickness, and one
layer will do. Further, if not needed, it may be omitted. The under
layer 4 is used as a under film for controlling the crystal
orientation of a magnetic layer formed thereon. As the under layer,
used is a thin film of a Cr-group alloy such as non-magnetic Cr--V,
Cr--Ti, Cr--Mo, Cr--Si, Cr--Mo--Ti alloy forming an irregular solid
solution which has good crystal consistency with the magnetic film
and may be (100) orientated. When simultaneously 0.5 vol. % to 50
vol. % nitrogen is added to the gas for discharge used in
sputtering to form the under layer, the crystal grains of the under
layer are refined. As a result, the crystal grains of the
continuously formed magnetic layer are also refined so that medium
noise can be reduced.
[0043] As the magnetic layer 5, not only Co--Cr--Pt--Ta alloy, but
a multi-alloy family material in which Co is taken as principal
component, Pt is contained to increase the coercive force, and
further Cr, Ta, SiO.sub.2, Nb and the like to reduce medium noise
are added may be used. Especially, when Ta, Nb, V, and Ti are
added, the melting point of a target is lowered, and composition
separation of the magnetic film containing Cr is easy to progress.
This is favorable.
[0044] In the Co-group alloy family material to which Pt, Ni or Mn
is added, lowering of magnetic anisotropic energy is less than that
in the case of other additive elements, so it is practical. To be
concrete, in addition to Co--Cr--Pt, used are alloys such as
Co--Cr--Pt--Ta, Co--Cr--Pt--SiO.sub.2, Co--Cr--Pt--Mn,
Co--Cr--Nb--Pt, Co--Cr--V--Pt, Co--Cr--Ti--Pt, Co--Cr--Nb--Ta--Pt,
Co--Pt--Ni--SiO.sub.2 and the like.
[0045] Concerning the composition of a Co alloy layer occupying a
ferromagnetic portion, it is considered that the solid solution
limit of Cr is 5 to 10 at. %, and the solid solution limit of Ta is
about 2 at. %, and a Co alloy magnetic layer is formed exceeding
these solid solution limits, whereby the magnetic separation in the
magnetic layer progresses to reduce medium noise. As a practical
composition, for example, the followings are used:
[0046] Co-20 at. % Cr-4 at. % Ta-8 at. % Pt alloy;
[0047] Co-22 at. % Cr-20 at. % Pt alloy;
[0048] Co-15 at. % Cr-8 at. % Pt-20 mol. % SiO.sub.2 alloy;
[0049] Co-17 at. % Cr-12 at. % Pt-5 at. % Mn alloy;
[0050] Co-17 at. % Cr-5 at. % Nb-10 at. % Pt alloy;
[0051] Co-20 at. % Cr-5 at. % V-12 at. % Pt alloy;
[0052] Co-20 at. % Cr-10 at. %-15 at. % Pt alloy;
[0053] Co-15 at. % Cr-5 at. % Nb-5 at. % Ta-20 at. % Pt alloy.
[0054] The above substrate is transported without being taken out
from the vacuum vessel to a protective coating layer forming
chamber 21 shown in FIG. 2. The protective coating forming chamber
21 is formed by an ion gun including a heat filament 22, an anode
23 and a grid 24 disposed in front of the heat filament. While the
protective coating forming chamber 21 is evacuated by a
turbo-molecular pump, from the rear of the anode, 15 sccm (Standard
Cubic centimeter per minutes) of Ar gas, 50 sccm of ethylene
(C.sub.2H.sub.4) gas, further 20 sccm of carbon dioxide (CO.sub.2)
gas, 10 sccm of nitrogen dioxide (NO.sub.2) gas and 10 sccm of
laughing gas (N.sub.2O) are introduced through a mass flow
controller. At this time, the pressure is about 0.5 Pa(4 mTorr) at
the baratron gauge.
[0055] Subsequently, 30 A is applied to the heat filament of the
ion guns positioned on both sides of the substrate, DC+100V is
applied to the anode to induce plasma, and then -530V is applied to
the grid to derive ions. Further, pulse bias with -100V and 3 kHz
is applied to the substrate. At this time, the anode current is 500
mA, and the bias current of the substrate is 50 mA. By this ion
beam deposition method (IBD) , a DLC protective coating layer 6
mainly composed of carbon and hydrogen is formed 3 nm thick on the
Co--Cr--Ta--Pt alloy layer 5. The deposition rate of coating at
this time is 1.0 nm/s.
[0056] By the above method, plural discs are manufactured, some of
them are subjected to thin film analysis, and the other are
provided with a lubricant layer 7 of fluorocarbon family. The
thickness of the layer is 2.2 nm measured by quantitative analysis
using Fourier-Transform InfraRed spectroscopic analyzer (FT-IR).
After that, floating check is performed to make a sliding test in a
single plate, or the disc is built in the magnetic disc apparatus
to make a reliability test.
[0057] The protective coating of the disc manufactured by the above
method is analyzed by the following methods to measure the
proportion of functional groups of the protective coating surface.
That is, ESCA (Electron Spectroscopy for Chemical Analysis) is used
for identifying the covering rate of the functional groups of the
protective coating surface. Direct identification of --COOH,
--C.dbd.O, --COH, --CNH.sub.2 which are surface functional groups,
using ESCA is difficult in view of sensitivity and measurement
accuracy. The above problems have been overcome by the tag
modification method described in the following.
[0058] That is, the covering rate identification is performed by
modification (tag modification) using molecules which have
functional groups interacting with the protective coating surface
functional groups quantitatively and irreversibly by molecular
recognition, and contain fluorine atoms which have high sensitivity
coefficient to ESCA.
[0059] To be concrete,
[0060] To identify --COOH functional group, the protective coat
surface is dipped in a benzene solution of pentafluorophenyl
bromide for one hour to modify --COOH functional group with
fluorine molecules.
[0061] To identify --C.dbd.O functional group, the protective
coating surface is dipped in an ethanol solution of
pentafluorophenylhydrazine for one hour to modify --C.dbd.O
functional group with fluorine molecules.
[0062] To identify --COH functional group, the protective coating
surface is dipped in an ethanol solution of
perfluorooctyldimethylchlorosilane to modify --COH functional group
with fluorine molecules.
[0063] To identify --CNH.sub.2 functional group, the protective
coating surface is dipped in a chloroform solution of
pentafluorobenzoylchloride for one hour to modify --CNH.sub.2
functional group with fluorine molecules.
[0064] The respective protective coating surface tag-modified by
one hour reaction at room temperature are dipped in the respective
solvents to remove unreacted material from the protective coating
surface.
[0065] In identifying the functional group covering rate of the
protective coating surface, each tag-modified protective coating
surface is obtained at an angle 24.degree. of analysis of ESCA by
Cls and Fls measurement intensity ratio, and as a result, the
proportion of the functional groups --COOH, --C.dbd.O, --COH,
--CNH.sub.2 per 100 carbon atoms is about 30% on the average in
total.
[0066] On the other hand, the disc provided with a lubricant is
attached on an evaluating apparatus having a head load/unload
mechanism to make a test. When load/unload test on ten discs are
made 50000 times at a rotating speed of 15000 r.p.m, tests on all
of ten discs are ended without crash. Further, when the thickness
of the lubricating layer of the tested disc is measured by FT-IR,
it is confirmed that the thickness is hardly decreased, 2.1 nm. As
a result, it is proved that the magnetic recording medium of the
invention has reinforced bonding force to the lubricant so that a
decrease in lubricant due to spin-off is small, and even in the
case where the thickness of the protective coating is very thin, 3
nm, sliding resisting reliability is sufficient. The above
evaluation result is described as sample No. 1 in FIG. 3.
COMPARATIVE EXAMPLE
[0067] Sample No. 2 is manufactured by the substantially same
method as that of the embodiment 1 except that 10 sccm of carbon
dioxide (CO.sub.2) gas and nitrogen oxide (NO.sub.2) gas and
dinitrogen monoxide are not added at the time of forming the
protective coating layer 6. The thickness of the protective coating
layer 6 is 3 nm which is the same as that of the embodiment 1, and
similarly the thickness of the lubricating layer 7 is 2.2 nm. The
thus manufactured disc is evaluated by the same method as that of
the embodiment 1.
[0068] As a result, in the tag modification analysis, the
proportion of the surface functional group is 13%. When load/unload
test is made on ten discs at the rotating speed of 15000 r.p.m, all
of the discs cause crash during the time from 1000 times to 8000
times. When the thickness of the lubricating layer is measured on
ten discs by FT-IR, it is confirmed that the thickness is decreased
to 0.7 to 1.2 nm as compared with that before the test.
[0069] As a result, it is known that in the magnetic recording
medium obtained by the manufacturing method of the comparative
example, the bonding force between the protective coating layer and
the lubricating layer is not enough so that the lubricating layer
is scattered and decreased due to high speed rotation, and the
frictional force between the magnetic recording medium and the
magnetic head is increased to cause crash.
[0070] <Embodiment 2>
[0071] When 5,0000 times load/unload tests are executed on the disc
described in the embodiment 1, in all of the magnetic recording
medium taking the thickness of the magnetic film to be 15 nm, 17 nm
and 21 nm, the magnetic recording media and the magnetic head are
not broken down, so favorable sliding resistance reliability is
obtained.
[0072] By decreasing the thickness of the magnetic layer, the
product Br.times.t of the thickness (t) of the magnetic layer and
the residual magnetic flux density Br is largely decreased. The
in-plane coercive force Hc approximately ranges from 176 kA/m to
256 kA/m, the coercivity squareness S* is from 0.74 to 0.65, about
0.7, and the remanence squareness is 0.78 to 0.7 (the remanence
squareness S is the ratio of the residual flux density to the
saturated flux density). These magnetic characteristics are
measured at 25.degree. C. by a sample vibration type
magnetometer.
[0073] The electromagnetic transducing characteristics of these
magnetic recording medium are measured by using a magnetic head
constructed so that the shield gap length Gs of the
magnetoresistive reproducing element (MR element) is 0.12 .mu.m and
the gap length of the write element is 0.2 .mu.m. The sense current
of the MR element is set to 3 mA, and the write current I is set to
41 mA. The floating height of the head is varied by changing the
rotating seed of the magnetic recording medium (magnetic disc
medium) to measure the output half width PW 50 of a solitary
reproduced wave by a digital oscilloscope (Tektronix TDS 544).
[0074] The thinner the magnetic film is, and the lower the floating
height of the magnetic head is, the smaller the PW 50 is. In the
case where the thickness of the magnetic film is 15 nm and the
floating height of the head is 25 nm, a small value, 240 nm is
obtained. The output at the maximum track recording density of 360
kFCI measured by the spectral analyzer is 1 to 2% of the output of
a solitary reproduced wave at 10 kFCI measured by the digital
oscilloscope. The output at the maximum track recording density of
360 kFCI measured by the spectral analyzer is integrated and
obtained until it exceeds the output of waveform of the odd order
by 100 MHz.
[0075] Further, the ratio SLF/Nd of the integrated medium noise
(Nd) in the case where 0-p output (SLF) of the solitary reproduced
wave and a signal of 360 kFCI are recorded is evaluated. The
floating height of the head is taken as 25 nm, and Nd is taken as
the integrated value of noise of a band corresponding to from 0.5
kFCI to 540 kFCI. In all of media, a high SLF/Nd ratio above 24 dB
is obtained at the high recording density as much as 360 kFCI.
[0076] FIG. 4 shows the constitution of the magnetic storage
apparatus including the magnetic disc medium 61, a driving part 62
for driving the magnetic recording medium, a magnetic head 63
formed by a recording part and a reproducing part, a unit 64 for
moving the magnetic head relatively to the magnetic recording
medium, a signal input unit for inputting a signal to the magnetic
head, a recording reproducing signal processing unit 65 for
reproducing an output signal from the magnetic head, and a part 66
serving as a refuge place at the time of loading and unloading the
magnetic head.
[0077] The reproducing part of the magnetic head is formed by a
magnetoresistive head. FIG. 5 is a typical perspective view of the
magnetic head used in measurement. The head is a composite head
having both an electromagnetic induction type head for recording
and a magnetoresistive head which are formed on a substrate 601.
The recording head is formed by an upper recording magnetic pole
603 and a combined lower recording magnetic pole and upper shield
layer 604 which sandwich coils 602, and the gap length between the
recording magnetic poles is 0.3 .mu.m. For the coil, copper 3 .mu.m
thick is used. The reproducing head is formed by a magnetoresistive
sensor 605 and electrode patterns 606 at both ends thereof, the
magnetoresistive sensor is sandwiched by the combined lower
recording magnetic pole and upper shield layer 604 and a lower
shield layer 607 which are 1 .mu.m thick, and the distance between
the shield layers is 0.20 .mu.m. In FIG. 6, the gap layer between
the recording magnetic pole, and the gap layer 608 between the
shield layer and the magnetoresistive sensor 608 are omitted.
[0078] FIG. 6 shows the structure of the section of the
magnetoresistive sensor. The signal detection area 701 of the
magnetic sensor is formed by a portion where a lateral bias layer
702, a separation layer 703 and a magnetoresistive ferromagnetic
layer 704 are sequentially formed on a gap layer 700 of aluminum
oxide. Ni--Fe alloy 20 nm thick is used in the magnetoresistive
ferromagnetic layer 704. Though Ni--Fe--Nb alloy 25 nm thick is
used in the lateral bias layer 702, any ferromagnetic alloy such as
Ni--Fe--Rh and the like may be used if the electric resistance is
comparatively high and soft magnetic characteristic is
favorable.
[0079] The lateral bias layer 702 is magnetized by a magnetic field
formed by a sense current flowing through the magnetoresistive
ferromagnetic layer 704 in the film in-plane direction (lateral
direction) vertical to the current, and lateral bias magnetic field
is applied to the magnetoresistive ferromagnetic layer 704. Thus,
selected is a magnetic sensor showing the linear reproduction
output to the leakage magnetic field from the medium 61. In the
separation layer 703 for preventing effective shunt current of
sense current from the magnetoresistive ferromagnetic layer 704, Ta
having comparatively high electric resistance is used, and the film
thickness is taken as 5 nm.
[0080] Both ends of the signal detection area are provided with a
taper part 705 worked to be tapered. The taper part 705 is formed
by a permanent magnet layer 706 for making the magnetoresistive
ferromagnetic layer 704 into single magnetic domain, and a pair of
electrodes 606 formed thereon for taking a signal. It is necessary
that the permanent magnet layer 706 has large coercive force and
the magnetizing direction is not easily changed, and an alloy such
as Co--Cr, Co--Cr--Pt or the like is used.
[0081] The magnetic storage apparatus shown in FIG. 4 is formed by
combining the magnetic recording medium described in the embodiment
1 with the head shown in FIG. 5. As a result, in the floating
system in which the magnetic floating height hm is about 48 to 60
nm, when the product Br.times.t of the thickness (t) of the
magnetic layer and the residual flux density Br measured by
applying a magnetic field in the relative running direction of the
magnetic head to the magnetic recording medium in recording exceeds
9.6 mA (120 gauss micron), satisfactory writing cannot be
performed, the overwrite characteristic is deteriorated, and the
output especially in the high track recording density area is also
lowered.
[0082] On the other hand, when Br.times.t is smaller than 32 mA (40
gauss micron), in some case, it is found that being left at
70.degree. C. for four days, the reproduction output is decreased
in some composition or thickness of the recording layer of the
medium. Accordingly, the magnetic storage apparatus is constructed
so that the product Br.times.t of the thickness (t) of the magnetic
layer and the residual magnetic flux density Br measured by
applying a magnetic field in the relative running direction of the
magnetic head to the magnetic recording medium in recording
mentioned in the magnetic recording medium described in the
embodiment 1 ranges from 3.2 mA (40 gauss micron) to 9.6 mA (120
gauss micron) both inclusive.
[0083] In the case where the magnetoresistive sensor part of the
magnetoresistive head uses a head formed between two shield layers
which are spaced from each other at a distance of 0.2 .mu.m and
made of soft magnetic substance, when the maximum track recording
density exceeds 250 kFCI, sufficient reproduction output cannot be
obtained. When the distance between two shield layers made of soft
magnetic substance is below 0.12 .mu.m, the element cannot be
formed easily because of difficulty in process machining.
Accordingly, the magnetic storage device is formed by using a head
formed between two shield layers which are spaced from each other
at a distance ranging from 0.12 .mu.m to 0.2 .mu.m both inclusive
and made of soft magnetic substance. By the thus constructed
magnetic storage apparatus, the recording density equal to or
higher than 50 giga bit per 1 in.sup.2 can be realized.
[0084] <Embodiment 3>
[0085] A magnetic storage apparatus is formed by the same
constitution as that of FIG. 4 except that instead of the
magnetoresistive head used in the embodiment 2, the
magnetoresistive head 63 described in the embodiment 2 uses a
magnetic head formed by a magnetoresistive sensor including plural
conductive magnetic layers which cause a large resistance change
due to a relative change in mutual magnetizing directions by an
external magnetic field and a conductive non-magnetic layer
disposed between the conductive magnetic layers.
[0086] FIG. 7 shows the sectional view of the used sensor. The
sensor has a structure in which a Ta buffer layer 801 5 nm thick, a
first magnetic layer 802 with a thickness of 7 nm, an intermediate
layer 803 made of copper 1.5 nm thick, a second magnetic layer 804
3 nm thick, and a Fe-50 at. % Mn antiferromagnetic alloy layer 805
10 nm thick are sequentially formed on a gap layer 608. In the
first magnetic layer 802, Ni-20 at. % Fe alloy is used, and in the
second magnetic layer 804, cobalt is used.
[0087] By exchange magnetic field from the antiferromagnetic layer
805, the magnetization of the second magnetic layer 804 is fixed in
one direction. On the contrary, the direction of the first magnetic
layer 802 which is in contact with the second magnetic layer 804 by
intercalating the non-magnetic layer 803 is varied by the leakage
magnetic field from the magnetic recording medium 61 so that the
resistance change is caused.
[0088] Such resistance change caused by a change in the relative
direction of magnetization of two magnetic layers is called spin
valve effect. In the present embodiment, a spin valve head
utilizing the effect for the reproducing head is used. The taper
part 705 has the same constitution as that of the magnetic sensor
of the embodiment 2.
[0089] The Br.times.t of the magnetic recording medium used in
measurement is taken as 3, 3.2, 4, 6, 8, 10, 12, and 14 mA. In the
case where Br.times.t is taken as 3 mA (37.5 gauss micron),
lowering of a reproducing signal caused with the passage of time is
extreme, and it is difficult to obtain practically favorable
coercive force. When Br.times.t exceeds 12 mA (150 gauss micron),
though the output of 2 F is large, the tendency of lowering the
output resolution becomes remarkable so that it is not
favorable.
[0090] When such a spin valve reproducing head is used, as
described in the embodiment 2, a signal recorded at the maximum
track recording density exceeding 360 kFCI is stably reproduced to
obtain signal output.
[0091] The head shown in here is the same as the head used in the
embodiment 2, and the magnetoresistive head is formed on the
magnetic head slider constructed so that the area of the floating
surface rail is equal to or smaller than 1.4 mm.sup.2 and the mass
is equal to or less than 2 mg. Setting the area of the floating
surface rail equal to or smaller than 1.4 mm.sup.2 reduces the
probability of colliding with the projection, and simultaneously
setting the mass equal to or less than 2 mg can improve shock
resistance reliability. Thus, high recording density and high shock
resistance can be reconciled, and the average failure time interval
(MTBF) equal to or longer than 30,0000 hours at the recording
density equal to or higher than 50 giga bit per 1 in.sup.2 can be
realized.
[0092] According to the invention, the bonding performance between
the protective coating and the lubricating film can be reinforced.
Furthermore, a mass-stored and high reliability magnetic disc
apparatus can be provided by combining the magnetic recording
medium with the magnetic head.
* * * * *