U.S. patent application number 09/379462 was filed with the patent office on 2001-07-26 for magnetic recording medium and magnetic recording apparatus using the same.
Invention is credited to FUTAMOTO, MASAAKI, HIRAYAMA, YOSHIYUKI, HONDA, YUKIO, INABA, NOBUYUKI, ITO, KENYA, YOSHIDA, KAZUETSU.
Application Number | 20010009730 09/379462 |
Document ID | / |
Family ID | 27472244 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009730 |
Kind Code |
A1 |
FUTAMOTO, MASAAKI ; et
al. |
July 26, 2001 |
MAGNETIC RECORDING MEDIUM AND MAGNETIC RECORDING APPARATUS USING
THE SAME
Abstract
Magnetic recording medium includes at least two layers having
different magnetic anisotropy constants formed on a substrate and
the perpendicular magnetic anisotropy of the second magnetic film
of those magnetic films, far from the substrate surface, made equal
to or larger than that of the first magnetic film near to the
substrate surface, thus improving the magnetic isolation of the
first magnetic film near to the substrate surface.
Inventors: |
FUTAMOTO, MASAAKI;
(KANAGAWA-KEN, JP) ; INABA, NOBUYUKI; (HASUDA-SHI,
JP) ; HIRAYAMA, YOSHIYUKI; (KODAIRA-SHI, JP) ;
HONDA, YUKIO; (FUCHU-SHI, JP) ; YOSHIDA,
KAZUETSU; (HIDAKA-SHI, JP) ; ITO, KENYA;
(HACHIOJI-SHI, JP) |
Correspondence
Address: |
JOHN C ALTMILLER
1500 K STREET NW SUITE 700
WASHINGTON
DC
200051257
|
Family ID: |
27472244 |
Appl. No.: |
09/379462 |
Filed: |
August 24, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09379462 |
Aug 24, 1999 |
|
|
|
09085861 |
May 28, 1998 |
|
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Current U.S.
Class: |
428/832 ;
G9B/5.241 |
Current CPC
Class: |
Y10T 428/12465 20150115;
Y10T 428/2495 20150115; Y10T 428/12875 20150115; Y10T 428/26
20150115; G11B 5/66 20130101; Y10T 428/12861 20150115; H04B 10/504
20130101; Y10T 428/24975 20150115; Y10T 428/265 20150115; Y10T
428/24942 20150115; Y10S 428/90 20130101 |
Class at
Publication: |
428/694.0TM |
International
Class: |
G11B 005/667 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 1997 |
JP |
09-139655 |
Jun 3, 1997 |
JP |
09-144835 |
Sep 30, 1997 |
JP |
09-265445 |
Claims
What is claimed is:
1. A magnetic recording apparatus using magnetic recording media
comprising: a non-magnetic substrate, an under layer, a
perpendicular magnetization film made of a Co-based alloy, an
intermediate layer made of a non-magnetic material having hexagonal
closed packed structure or a weak ferromagnetic material of which
the saturation magnetization is 100 emu/cc or below in contact with
said perpendicular magnetization film on said substrate side, and
at least two different magnetic films successively formed on said
perpendicular magnetization film, said magnetic films being soft
magnetic films or magnetic films having longitudinal magnetic
anisotropy, the total thickness of said perpendicular magnetization
film and said two different magnetic films being 100 nm or below,
and the thickness of said perpendicular magnetization film being
larger than the thickness of said magnetic films formed
thereon.
2. A magnetic recording apparatus according to claim 1, and further
including a ring-type inductive magnetic head.
3. A magnetic recording apparatus according to claim 1 wherein said
media is information recording media, and further including a
thin-film ring-type inductive head for writing, and a
high-sensitive sensor including a magneto-resistive effect device
or a giant magneto-resistive effect device for reading so that
magnetic recording can be made at a longitudinal recording density
of 5 Gb/in.sup.2 or above.
4. A magnetic recording apparatus according to claim 1, wherein
said media is information recording media, and further including a
thin-film ring-type inductive head for writing, and a
high-sensitive sensor including a magnetic tunnel effect device for
reading, so that the magnetic recording/reproduction can be made at
a longitudinal recording density of 20 Gb/in.sup.2 or above.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to perpendicular magnetic
recording medium which are small in read back noise and suitable
for high-density magnetic recording, and to a magnetic recording
apparatus using these media.
[0002] The currently used practical magnetic recording system is
the longitudinal magnetic recording system in which magnetic
recording is made in parallel to the surface of the magnetic
recording medium, and so that the magnetic N-poles are opposed one
to one and that the magnetic S-poles are opposed to one to one. In
order to increase the linear recording density in the longitudinal
magnetic recording, it is necessary that the coercivity be
increased by decreasing the product of residual flux density (Br)
and magnetic film thickness (t) of the magnetic film of a recording
medium to reduce the effect of the demagnetizing field at the
magnetic recording process. In addition, to decrease the medium
noise caused by magnetization transition, it is necessary to orient
the magnetic easy axis of the magnetic film in the direction
parallel to the substrate surface, and to control the crystal grain
size. To control the crystal orientation and grain size of the
magnetic thin film, an underlayer for structure control is formed
between the substrate and the magnetic film.
[0003] As the magnetic film, a Co-based alloy thin film is used
which chiefly contains cobalt Co, and has an element such as Cr,
Ta, Pt, Rh,. Pd, Ti, Ni, Nb, Hf added to the cobalt. The Co-based
alloy of the magnetic thin film is chiefly made of a material of
hexagonal closed packed structure (hereinafter, referred to as hcp
structure). The magnetic easy axis is present in the directions of
c-axis, <0, 0.1> and is oriented in the longitudinal
direction. An underlayer for structure control is formed between
the substrate and the magnetic film in order to control the crystal
orientation and grain size of the magnetic film. The underlayer is
made of a material which chiefly contains Cr and has an element of
Ti, Mo, V, W, Pt, Pd added to Cr. The magnetic thin film is formed
by vacuum evaporation or sputtering. As described above, the
product of residual flux density (Br) and magnetic film thickness
(t) of the magnetic film is required to be reduced in order to
reduce the medium noise in the longitudinal magnetic recording and
to thereby increase the linear recording density. For this purpose,
it has been considered that the magnetic film thickness is reduced
to 20 nm or below, and that the crystal grain size is greatly
reduced. However, such medium has a very important problem that the
recording magnetization is reduced by thermal instability. This
phenomenon interferes with the high-density recording.
[0004] The presently used magnetic disk recording apparatus is of
the longitudinal magnetic recording system. The technical subject
is that the longitudinal domains parallel to the substrate are
formed at high density in the longitudinal magnetic recording
medium which is easy to be magnetized in the direction parallel to
the disk substrate surface. A method of increasing the recording
density in the longitudinal magnetic recording medium is proposed,
which employs keepered media formed by depositing an extremely thin
soft magnetic film on the recording medium that have the magnetic
easy axis in the longitudinal direction.
[0005] This technique is described in Abstracts, page 116 (paper
No. DQ-13) and pages 133-134 (paper No. EB-12) published in the
41st Annual Conference on Magnetism & Magnetic Materials (Nov.
12-15, 1996).
[0006] In such documents, it is described that if this media
structure is employed it will be possible to increase the
longitudinal magnetic recording density to 1 Gb/in.sup.2 or above
by use of thin film heads of self-recording/reproduction system. In
the longitudinal recording system, however, since the adjacent
recorded bits are substantially magnetized to oppose to each other,
magnetization transition regions of certain widths are formed
across the boundaries even when this technique is employed. Thus,
it will be technically difficult to record at a longitudinal
density of 5 Gb/in.sup.2 or above.
[0007] On the other hand, the perpendicular magnetic recording
system forms domains on the recording medium surface
perpendicularly, and so that the adjacent recorded bits are
unti-parallel to each other. This system has the advantage that the
demagnetizing field at the boundary between the recorded bits is
decreased, and thus it is one of the powerful means for
high-density magnetic recording.
[0008] For the longitudinal high-density recording, it is necessary
that the magnetic film be formed to have a thickness of 20 nm or
below as described above. In this case, there is a problem that the
recorded magnetization regions may be lost by thermal instability.
On the contrary, the perpendicular magnetic recording system is
able to form the magnetic film thicker than the longitudinal
magnetic recording system, and thus stably maintain the recorded
magnetization regions. In order to reduce the media noise generated
from the magnetization transition and increase the linear recording
density in the perpendicular recording system, it is necessary to
orient the magnetic easy axis of the magnetic film perpendicularly
to the substrate surface, and control the crystal grain size.
[0009] As the magnetic film, a Co-based alloy thin film is used
which chiefly contains cobalt Co and has an element of Cr, Ta, Pt,
Rh, Pd, Ti, Ni, Nb, Hf added to Co. The Co-based alloy of the
magnetic thin film is chiefly made of a material of hexagonal
closed packed structure (hereinafter, referred to as hcp
structure). The magnetic easy axis is present in the directions of
c-axis, <0, 0.1> and is oriented in the perpendicular
direction. The magnetic thin film is formed by vacuum evaporation
or sputtering. In order to increase the linear recording density at
the time of recording and the read output and reduce the read back
noise so that the magnetic recording characteristics can be
improved, it is necessary to improve the perpendicular orientation
of the c-axis of the Co-based alloy thin film and control the
crystal grain size. Thus, it has so far been considered that an
underlayer for structure control is formed between the substrate
and the magnetic film.
[0010] The perpendicular magnetic recording system has attracted a
great deal of attention as a system capable of high-density
magnetic recording, and structure of medium suitable for the
perpendicular magnetic recording have been proposed. A method of
providing a non-magnetic underlayer between the perpendicular
magnetization film and the substrate has been examined in order to
improve the perpendicular orientation of the perpendicularly
magnetized film made of a Co-based alloy material. For example, a
method of depositing a Ti film as an underlayer for a Co--Cr
magnetic film is described in JP-A-58-77025, and JP-A-58-141435, a
method of providing an under layer made of Ge, Si material in
JP-A-60-214417, and a method of providing an underlayer made of an
oxide material such as CoO, NiO in JP-A-60-064413. In addition, a
magnetic recording medium having a soft magnetic layer of Parmalloy
provided between the substrate and the perpendicular magnetization
film has been considered as a perpendicular magnetic recording
medium which is used in combination with a single-pole type
magnetic recording head.
[0011] However, in order to achieve ultra-high density magnetic
recording of several Gb/in.sup.2 or above, particularly more than
10 Gb/in.sup.2, it is important to reduce the noise contained in
the read output signal, particularly the medium noise caused by the
micro-structure of the medium in addition to the improvement of the
linear recording density. Thus, it is necessary to more highly
control the thin film structure in addition to the crystal
orientation of the magnetic film. The media noise has so far been
tried to reduce by various ways. For example, these ways are (1) to
segregate the non-magnetic element Cr of CoCr-based alloy in the
crystal grain boundary or grains in order to suppress the magnetic
mutual action between the magnetic grains and (2) to isolate the
magnetic grains in a form by controlling the sputtering gas
pressure. The improvement in medium structure by these conventional
techniques was effective in reducing the medium noise, but the
reverse magnetic domains formed opposite to the magnetization
direction and the associated magnetization irregularity, which
cause the medium noise in the perpendicular magnetic recording, was
not able to be reduced effectively.
[0012] The perpendicular magnetic recording medium capable of
high-density magnetic recording of 5 Gb/in.sup.2 or above is
required to have small medium noise in addition to high linear
recording density or resolution. There are some reported examples.
As for example described in a paper titled "Improvement in S/N
ratio of Single Layer perpendicular Magnetic Disk Media" of the
Fifth Perpendicular Magnetic Recording Symposium (Oct. 23-25,
1996), pp. 98-103, it is effective to decrease the thickness of the
perpendicular magnetization film, introduce a non-magnetic
underlayer of CoCr between the perpendicular magnetization film and
the substrate, add a non-magnetic element such as Ta to the Co
alloy magnetic film and/or reduce the magnetic crystal grain size.
These countermeasures are able to considerably reduce the medium
noise, but if the noise can be more decreased, the recording
density of the magnetic recording apparatus will be easily
increased much more.
[0013] Accordingly, it is an object of the invention to remove the
drawbacks of the prior art, and provide perpendicular magnetic
recording media having excellent low-noise characteristics and
suitable for ultra-high density magnetic recording by controlling
the perpendicular magnetic anisotropy, crystal orientation or
mutual action between the magnetic grains of the perpendicular
magnetization film formed on the substrate to thereby control the
fine domain structure magnetically recorded, and a magnetic
recording apparatus using the medium.
[0014] According to the invention, the perpendicular magnetic
recording medium having the low-noise characteristics can achieve
high-density recording of 5 Gb/in.sup.2 or above, and thus make it
easy to produce high-density recording apparatus.
[0015] After examining the recorded magnetization structure of the
perpendicular magnetic recording medium by a magnetic force
microscope and a spin-polarized scanning electron microscope, it
was found that most of the noise are caused by reverse magnetic
domains and microscopic instability of magnetization present in the
medium surfaces. In order to decrease the medium noise, it is
necessary to reduce the reverse magnetization and microscopic
instability of magnetization present in the medium surfaces.
SUMMARY OF THE INVENTION
[0016] It is an object of the invention to provide perpendicular
magnetic recording medium having both low- noise characteristics
and high-density linear recording characteristic which enable the
high-density magnetic recording of 5 Gb/in.sup.2 or above, and
magnetic recording/reproducing apparatus using the medium.
[0017] According to the invention, at least two magnetic films
which are different in perpendicular magnetic anisotropy are formed
on the substrate, and in this case the perpendicular magnetic
anisotropy of the second magnetic film on the side far from the
substrate is made greater than that of the first magnetic film on
the side near to the substrate surface, thereby improving the
magnetic isolation of the first magnetic film on the side near to
the substrate surface. That is, the above object can be achieved by
assigning a different role to each magnetic film as they say.
[0018] After examining the recorded magnetization structure by a
magnetic force microscope or spin-polarized scanning electron
microscope, it was found that most of the noise are caused by the
reverse magnetic domains and microscopic instability of
magnetization present in the medium surfaces. In order to decrease
the medium noise, it is necessary to reduce the reverse magnetic
domains and microscopic instability of magnetization present in the
medium surfaces. To decrease the medium noise and assure
high-density linear recording characteristics, it is desired to
reduce the magnetic crystal grain size of the perpendicular
magnetic recording medium and magnetically isolate the grains.
[0019] From the results of experiments by the inventors, it was
found that the following media structure is effective in achieving
the above object.
[0020] First, referring to FIG. 1, a single-layer type
perpendicular magnetic recording medium is normally produced by
depositing a perpendicular magnetization film 13 on an underlayer
12 which is formed on a non-magnetic substrate 11 for the purpose
of improving the perpendicular orientation of the magnetic film and
controlling the crystal grain size. On this magnetization film,
there is usually deposited a protective film of carbon or the like.
The magnetic film is made of a Co-based alloy containing at least
one element selected from Cr, Ta, Pt, Pd, Si, V, Nb, W. Mo, Hf, Re,
Zr, B, P, Ru. This magnetic film is a polycrystalline film, and for
high-density linear recording characteristic and low-noise
characteristic, its crystal grain size is selected to be normally
20 nm or below, and a non-magnetic element is preferentially
segregated in the crystal grain boundary. This perpendicular
magnetization film has a small magnetic exchange coupling force in
the longitudinal direction because the segregated layer exists in
the crystal grain boundary.
[0021] The present inventors found that the effective way to
further reduce the medium noise is to provide on the first
perpendicular magnetization film 13 of Co-based alloy a second
perpendicular magnetization film 14 of which the magnetic exchange
coupling force in the longitudinal direction is greater than that
of the first perpendicular magnetization film. The second
perpendicular magnetization film 14 is preferably a multi-layered
perpendicular magnetization film of Co/Pt, Co/Pd, Co alloy/Pt, Co
alloy/Pd, Co alloy/Pt or Pd alloy or a noncrystal perpendicular
magnetization film of Tb Fe Co containing rare-earth elements.
[0022] The deposition of the second perpendicular magnetization
film 14 can reduce the magnetic instability present in the surface
of the first perpendicular magnetization film 13. Since the second
perpendicular magnetization film 14 has a large magnetic exchange
coupling force in the longitudinal direction, the microscopic
magnetic instability is not easily caused on the surface.
[0023] Here, in order to assure low-noise characteristics in the
perpendicular magnetic recording medium, it is necessary to
decrease the thickness of the second perpendicular magnetization
film 14 as compared with that of the first perpendicular
magnetization film 13. The thickness of the second perpendicular
magnetization film is preferably selected to be less than 1/3 that
of the first perpendicular magnetization film. The role of the
second perpendicular magnetization film 14 is not to hold the
perpendicular magnetic recording, but to greatly reduce the
microscopic magnetic instability in the surface of the first
perpendicular magnetization film 13. To assign this function to a
thin film, it is more desirable to provide high magnetic anisotropy
energy of 5.times.10.sup.6 erg/cc or above. When the thickness of
the second perpendicular magnetization film 14 is larger than that
of the first perpendicular magnetization film 13, the medium noise
is increased as compared with the case in which only the first
perpendicular magnetization film is deposited.
[0024] In order to achieve a recording density of 5 Gb/in.sup.2 or
above, the total thickness of the first and second perpendicular
magnetization films should be selected to be more than 7 nm and
less than 100 nm. If the total thickness is larger than 100 nm, the
magnetic crystal grains constituting the perpendicular
magnetization films are enlarged in volume, and as a result the
magnetic switching volume is also increased, thus causing large
medium noise. Accordingly, it is not possible to achieve the signal
to noise ratio for a recording density of 5 Gb/in.sup.2 or above.
If the total thickness is equal to or less than 7 nm, the recording
magnetization is remarkably deteriorated by thermal
instability.
[0025] The thickness of the second perpendicular magnetization film
is preferably more than 3 nm and less than 10 nm. If it is equal to
or less than 3 nm, the effect of reducing the magnetic instability
in the surface of the first perpendicular magnetization film is
unrecognizably small. If it is larger than 10 nm, the medium noise
is increased.
[0026] The object of the invention can also be achieved by
employing the structures shown in FIGS. 2 through 6. As to the
structure shown in FIG. 2, the second perpendicular magnetization
film 14 is deposited on the first perpendicular magnetization film
13 as in the case of FIG. 1, but between the first perpendicular
magnetization film 13 and the non-magnetic substrate 11 there are
formed an underlayer 23 of a nonmagnetic material having a
hexagonal closed packed structure or a weak ferro magnetic material
having a hexagonal closed packed structure of which the saturation
magnetization is 100 emu/cc or below, and the underlayer 12 for
controlling the crystal orientation of this underlayer film. Use of
these dual-underlayer structure will enable the first perpendicular
magnetization film to be highly controlled in its crystal grain
size and orientation, and low-noise characteristics to be
achieved.
[0027] The media structure, as shown by its cross-section in FIG.
3, has the first and second perpendicular magnetization films 13,
14 stacked, and also has another perpendicular magnetization film
33 of multi-layered structure or non-crystal structure formed
between the first perpendicular magnetization film 13 and the
underlayer 12. Thus, the magnetic instability present in the front
and back sides of the first perpendicular magnetization film 13 can
be reduced, so that low-noise characteristics can be achieved.
[0028] The cross-sectional structures shown in FIGS. 4 through 6
are structures of perpendicular magnetic recording media of the
type in which a soft magnetic layer is provided under the
perpendicular magnetization film as indicated by reference numeral
42. In this case, the second perpendicular magnetization film 14 of
multi-layered structure or amorphous-like structure is also
provided on the first perpendicular magnetization film 13 of Co
alloy.
[0029] Referring to FIG. 5, there is shown an underlayer film 53
having a non-magnetic hexagonal closed packed structure or a weak
ferro magnetic hexagonal closed packed structure of which the
saturation magnetization is 100 emu/cc or less. In FIG. 6, there is
shown a perpendicular magnetization film 64 of multi-layered or
amorphous structure.
[0030] The second perpendicular magnetization film of multi-layered
or amorphous structure is formed on the first perpendicular
magnetization film as shown in FIGS. 1 through 6. This second
perpendicular magnetization film serves to reduce the microscopic
magnetic instability present in the surface of the first
perpendicular magnetization film. The perpendicular magnetization
film of multi-layered or non-crystal structure formed under the
first perpendicular magnetization film as shown in FIGS. 3 and 6
acts to reduce the microscopic magnetic instability present in the
lower surface of the first perpendicular magnetization film.
[0031] The underlayer 12 in FIG. 1, the underlayer film 23, shown
in FIG. 2, of non-magnetic hexagonal closed packed structure or
weak ferro magnetic hexagonal closed packed structure of which the
saturation magnetization is 100 emu/cc or below, the underlayer 12
formed thereunder, the underlayer shown in FIG. 3, the under layer
53, shown in FIG. 5, of non-magnetic hexagonal closed packed
structure or weak ferro magnetic hexagonal closed packed structure
of which the saturation magnetization is 100 emu/cc or below, and
the underlayer 12 in FIG. 6 are all provided for the purpose of
controlling the crystal orientation and crystal grain size of the
magnetic films formed on these underlayers, respectively, thus
making it possible to improve the characteristics of the magnetic
films along their purposes. If the saturation magnetization of the
underlayer film exceeds 100 emu/cc, the medium noise will be
increased, and the recording resolution will be reduced, thus
adversely affecting the magnetic recording/reproduction
characteristics.
[0032] As to the cause of the reverse magnetic domain, if the
perpendicular magnetization film is perpendicularly magnetized in
one direction, an intense demagnetizing field is acted on the
medium surface, and this action of demagnetizing field produces the
so-called reverse magnetic domains in the direction opposite to the
perpendicularly magnetized direction. In order to suppress this
reverse magnetic domains from being produced, it is necessary to
employ a perpendicular magnetization film having magnetic
anisotropy energy. The magnetic anisotropy energy is desirably
2.5.times.10.sup.6 erg/cc or above.
[0033] The magnetic anisotropy energy of the perpendicular
magnetization film made of Co-based alloy easy to handle as
practical media is 5.times.10.sup.6 erg/cc. There is a Co-based
alloy regular lattice material having more magnetic anisotropy
energy than this value, but this material has difficulty in
reducing noise because too large media noise is caused by a strong
mutual action in the longitudinal direction of the magnetic
film.
[0034] The multi-layered perpendicular magnetization film of Pt/Co,
Pd/Co other than Co alloy or a perpendicular magnetization film of
amorphous structure containing rare earth elements such as TbFeCo
has magnetic anisotropy energy of 2.5.times.10.sup.6 erg/cc or
above and thus can be expected to attain the present subject.
However, the magnetic mutual action in the longitudinal direction
will also be strong as in the above description if no
countermeasure is provided, and hence the medium noise is large.
Thus, a special device is needed for reducing the media noise. In
addition, in order to increase the surface magnetic recording
density up to 5 Gb/in.sup.2 or above, the linear recording density
is required to be 250 kFCI or above. The bit length corresponding
to this linear recording density is 100 nm. The thickness of the
magnetic recording media for recording is desired to be less than
the minimum bit length. Thus, the thickness of the perpendicular
magnetization film is required to be 100 nm or below.
[0035] Since the reverse magnetic domains can be suppressed by use
of a perpendicular magnetization film of high magnetic anisotropy
energy, the medium noise due to the reverse magnetic domains can be
prevented from being produced. However, the medium noise is also
produced by a microscopic magnetic instability present in the
medium surfaces. If the magnetic mutual action in the longitudinal
direction of the magnetic film is large, a long-period magnetizing
instability is produced. In addition, it was found that if there is
magnetic heterogeneity in the surface of the perpendicular
magnetization film, a short-period magnetizing instability is
produced, thus causing the medium noise.
[0036] From the results of the experiments by the inventors, it was
found that in order to suppress these long-period, short-period
magnetic instability, it is necessary that a soft magnetic film or
a magnetic film having a magnetic easy axis in the longitudinal
direction be formed on the surface of the perpendicular
magnetization film. In this case, the thickness of the magnetic
films must be selected to be smaller than that of the perpendicular
magnetization film for recording. If the film thickness is large,
the magnetic flux produced from the recorded bits on the
perpendicular magnetization films makes closed magnetic circuits
absorbed by these films, and thus the magnetic flux does not leak
from the medium surfaces, so that the recorded signal cannot be
reproduced by magnetic heads.
[0037] If the thickness of these magnetic films is properly thin,
the long-period, short-period magnetic instability present in the
perpendicular magnetization film surfaces is absorbed by the
magnetic films formed on the surfaces of the perpendicular
magnetization films, but the strong magnetic flux generated from
the recorded bits cannot be absorbed enough. In this case, since
the magnetic flux caused by the magnetic instability does not leak
to the magnetic film surfaces, it cannot be detected by magnetic
heads, so that the medium noise is decreased. The combination of
the perpendicular magnetization film which absorbs the magnetic
flux due to the magnetic instability but little absorbs the
magnetic flux from the recorded bits, and the thickness of the
magnetic film provided on the surface depends on the thickness of
the perpendicular magnetization film, saturation magnetization,
coercivity and so on. Thus, it is necessary to select the most
suitable combination for each case.
[0038] The thickness of the magnetic film provided on the surface
should be confined within a range of generally 2 to 10 nm or
preferably 3 to 5 nm considering the factors such as controllable
ability for film production and for film thickness distribution in
all regions of disk surfaces. The magnetic film may be a soft
magnetic film of Parmalloy, Fe--Si, Fe--Si--Al, CoNbZr or other
materials or a magnetic film, of Co, Ni, Fe, CoNi, CoNiCr or the
like, which is easy to be magnetized in the longitudinal direction.
In addition, part of the surface of the perpendicular magnetization
film may be changed to a soft magnetic film or longitudinal
magnetization film by diffusing or implanting a light element such
as C, B, N or P into the surface.
[0039] FIG. 7 shows an example of the application of the invention
to a single-layered perpendicular magnetic recording medium.
[0040] In this single-layered perpendicular magnetic recording
medium, normally the underlayer 12 for improving the perpendicular
orientation of the magnetic film and controlling the crystal grain
size is deposited on the non-magnetic substrate 11, and a
perpendicular magnetization film 71 is formed on the underlayer. In
addition, a protective film of carbon or the like is normally
deposited on the magnetization film.
[0041] The magnetic film 71 is made of a Co-based alloy containing
at least one of Cr, Ta, Pt, Pd, Si, V, Nb, W, Mo, Hf, Re, Zr, B, P,
Ru. This magnetic film is a poly-crystal film of which the crystal
grain size is normally 20 nm or below and which has the structure
in which a non-magnetic element is preferentially segregated in the
crystal grain boundaries in order to attain high-density linear
recording characteristics and low noise characteristic. This
perpendicular magnetization film has a small magnetic exchange
coupling force because of the presence of the segregated layer in
the crystal grain boundaries, and a microscopic magnetic
instability because of the compositional segregation and
undulations in the media surfaces.
[0042] To reduce the medium noise, a soft magnetic film or
longitudinal magnetization film 72 which is thinner than the
thickness of the perpendicular magnetization film is deposited on
the perpendicular magnetization film 71. The perpendicular
magnetization film 71 may be a multi-layer type perpendicular
magnetization film made of Co/Pt, Co/Pd, Co alloy/Pt, Co alloy/Pd,
Co alloy/Pt or Pd alloy, or a amorphous type perpendicular
magnetization film containing a rare earth element such as TbFeCo
in place of being made of a Co-based alloy material.
[0043] When the soft magnetic film 72 is provided on the
perpendicular magnetization film 71, the magnetic flux generated
from the magnetic instability present in the surface of the
perpendicular magnetization film 71 is absorbed by the magnetic
film, and as a result the medium noise is decreased. In addition,
when a thin magnetic film is formed, the magnetic instability is
not easily generated even if microscopic undulations and
composition segregation are present in the surface. As shown in
FIG. 7, the protective film 15 is deposited on the magnetization
film.
[0044] In order to achieve a recording density of 5 Gb/in.sup.2 or
above, the total thickness of the perpendicular magnetization film
71 and soft magnetic film 72 is required to be confined within the
range of 7 nm to 100 nm. If the thickness is larger than 100 nm,
the volume of magnetic crystal grain constituting the film becomes
large, and as a result the magnetic switching volume is enlarged.
Thus, the medium noise is increased, degrading the signal to noise
ratio, so that a recording density of 5 Gb/in.sup.2 or above cannot
be attained. If the thickness is smaller than 7 nm, the recording
magnetization is remark- ably deteriorated by thermal
instability.
[0045] The object can also be achieved by use of the structures
shown in FIGS. 8 through 10. In the medium structure shown in FIG.
8, an underlayer 73 having a non-magnetic hexagonal closed packed
structure or a weak ferro hexagonal closed packed structure of 100
emu/cc or below is formed between the first perpendicular
magnetization film 71 and the non-magnetic substrate 11, and the
underlayer 12 is also formed under the underlayer 73 in order to
control the crystal grain orientation of the underlayer film 73. In
addition, the magnetic film 72 made of a thin soft magnetic film or
longitudinal magnetization film is deposited on the perpendicular
magnetization film 71. By this dual underlayer structure, it is
possible to highly control the crystal grain size and crystal
orientation of the perpendicular magnetization film, and hence to
attain low noise characteristics.
[0046] The structures shown by the cross-sectional views of medium
of FIGS. 9 and 10 are of the perpendicular magnetic recording
medium of the type in which a soft magnetic film layer is held
under the perpendicular magnetization film. As shown in FIGS. 9 and
10, a soft magnetic film layer 74 is formed on the substrate. In
this case, the magnetic film 72 of a soft magnetic film or having
longitudinal magnetic anisotropy is also formed on the
perpendicular magnetization film.
[0047] In FIGS. 7 through 10, the magnetic film formed on the
perpendicular magnetization film absorbs the magnetic flux
generated from the long-period, short-period magnetic instability
present in the surface of the perpendicular magnetization film,
thus serving to reduce the medium noise. The underlayer 12 in FIG.
7, the underlayer 73 having a non-magnetic hexagonal closed packed
structure or a weak ferro hexagonal closed packed structure of
which the saturation magnetization is 100 emu/cc or below, and the
underlayer 12 under it as shown in FIG. 8, and the underlayer 73 in
FIG. 10 are all provided for the purpose of controlling the crystal
orientation and crystal grain size of the magnetic film formed on
the underlayers. Thus, the magnetic film can be improved in the
characteristics.
[0048] In addition, the protective film 15 is formed as shown in
the figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] FIG. 1 is a cross-sectional view of one embodiment of a
magnetic recording medium according to the invention.
[0050] FIG. 2 is a cross-sectional view of another embodiment of a
magnetic recording medium according to the invention.
[0051] FIG. 3 is a cross-sectional view of another embodiment of a
magnetic recording medium according to the invention.
[0052] FIG. 4 is a cross-sectional view of another embodiment of a
magnetic recording medium according to the invention.
[0053] FIG. 5 is a cross-sectional view of another embodiment of a
magnetic recording medium according to the invention.
[0054] FIG. 6 is a cross-sectional view of another embodiment of a
magnetic recording medium according to the invention.
[0055] FIG. 7 is a cross-sectional view of another embodiment of a
magnetic recording medium according to the invention.
[0056] FIG. 8 is a cross-sectional view of another embodiment of a
magnetic recording medium according to the invention.
[0057] FIG. 9 is a cross-sectional view of another embodiment of a
magnetic recording medium according to the invention.
[0058] FIG. 10 is a cross-sectional view of another embodiment of a
magnetic recording medium according to the invention.
[0059] FIG. 11A to FIG. 11F are diagrams to which reference is made
in explaining a magnetic recording medium of the invention.
[0060] FIG. 12A to FIG. 12F are diagrams for comparing a magnetic
recording medium of the invention and conventional media.
[0061] FIG. 13A and FIG. 13B are plan views and cross-sectional
view of an embodiment of a magnetic recording apparatus according
to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0062] [Embodiment 1]
[0063] The magnetic recording medium having the cross-section shown
in FIG. 1 was produced by depositing films on a glass substrate of
2.5-inch diameter according to DC magnetron sputtering method. On
the substrate 11, there were formed in turn the underlayer 12, the
first perpendicular magnetization film 13, the second perpendicular
magnetization film 14, and the protective film 15. The underlayer
was deposited by use of a Ti-10 at % Cr target, the first
perpendicular magnetization film by a Co-19 at % Cr-8 at % Pt
target, the second perpendicular magnetization film by a target of
Co and Pt, and the protective film by a carbon target.
[0064] Under the conditions of a sputtering Ar gas pressure of 3 m
Torr, sputter power of 10 W/cm.sup.2, and substrate temperature of
250.degree. C., a TiCr film was formed up to a thickness of 30 nm,
the first perpendicular magnetization film up to 30 nm, a Co/Pt
multi-layered film of the second perpendicular magnetization film
up to 6 nm, and the carbon film up to 10 nm. As to the Co/Pt multi-
layered film of the second perpendicular magnetization film, a Co
target and a Pt target were alternately operated to grow a film of
1.5 nm in each part of one cycle, and thus the total thickness, 6
nm of the second perpendicular magnetization film was grown in two
cycles. Thus, the magnetic recording medium of which the
cross-section is shown in FIG. 1 was produced. Here, the anisotropy
energy of the first perpendicular magnetization film was
3.times.10.sup.6 erg/cc, and the anisotropy energy of the second
perpendicular magnetization film was 2.times.10.sup.7 erg/cc.
[0065] In addition, as the second perpendicular magnetization film,
multi-layered films of Co/Pd, Co-16 at % Cr/Pt, and Co/Pt-20 at %
Pd were grown up to the same thickness and structure as given
above. The perpendicular magnetization film of TbFeCo was also
formed to have the same thickness. Thus, different magnetic
recording medium were produced. The anisotropy energy of the second
perpendicular magnetization film for each case was 1.times.10.sup.7
erg/cc for Co/Pd, 1.2.times.10.sup.7 erg/cc for CoCr/Pt,
8.times.10.sup.6 erg/cc for Co/PtPd, and 6.times.10.sup.6 erg/cc
for TbFeCo. Moreover, magnetic recording medium of the same
structure, but having no second perpendicular magnetization film
were produced as samples for comparison.
[0066] The coercivity (Hc) and read/write characteristics of these
magnetic recording medium were evaluated by a vibrating sample
magnetometer (VSM) and a dual head with inductive head for writing
and with magnetoresistive (MR) head for reading. The gap length of
the record head was selected to be 0.2 .mu.m, the shield gap length
of the MR head for reading to be 0.2 .mu.m, and the spacing for
measurement to be 0.06 .mu.m. The half output decoding density
(D.sub.50), which corresponds to the half of the low-frequency read
output, was measured. The signal to noise ratio, S/N ratio for
magnetic recording at 20 kFCI was measured relative to the SIN
ratio of the samples for comparison. The measured results are shown
in Table 1.
1 TABLE 1 EXAMPLES FOR INVENTION COMPARISON UNDERLAYER Ti-Cr Ti-Cr
FIRST PERPENDICULAR FILM CoCrPt CoCrPt SECOND PERPENDICULAR FILM
Co/Pt Co/Pd CoCr/Pt Co/PtPd TbFeCo No COERCIVITY (kOe) 3.2 2.7 2.8
2.6 2.9 2.5 RECORDING DENSITY D.sub.50 (kFCI) 210 225 208 245 240
180 S/N (RELATIVE VALUE) 1.8 1.9 2.3 2.1 1.7 1
[0067] From the table, it was found that the magnetic recording
medium of this embodiment have larger D.sub.50 and S/N than the
samples for comparison and thus can be used as high-density
magnetic recording medium. In addition, a magnetic
recording/reproducing apparatus with MR head for reading was
produced which employs the 2.5-in diameter magnetic recording media
made according to this embodiment. This apparatus was operated
under the condition of 5.7 Gb/in.sup.2 in areal density. The result
was that the error rate can be confined within 1.times.10.sup.-9.
Thus, it was confirmed that this apparatus can be used as
ultra-high density magnetic recording/reproducing apparatus.
[0068] [Embodiment 2]
[0069] The magnetic recording medium having the cross-section shown
in FIG. 2 was produced by depositing films on a 2.5-in diameter
silicon substrate according to the DC magnetron sputtering method.
On the substrate 11, there were formed in turn the first underlayer
12, the second underlayer 23, the first perpendicular magnetization
film 13, the second perpendicular magnetization film 14 and the
protective film 15. The first underlayer was deposited by use of a
Ti-10 at % Cr target, the second-underlayer by a Co-35 at % Cr
target, the first perpendicular magnetization film by a Co-16 at %
Cr-8 at % Pt-3 at % Ta target, the second perpendicular
magnetization film by a target of Co and Pt, and the protective
film by a carbon target.
[0070] Under the conditions of a sputtering Ar gas pressure of 3 m
Torr, sputter power of 10 W/cm.sup.2, and substrate temperature of
280.degree. C., a CrTi film was formed up to a thickness of 30 nm,
a CoCr film up to 15 nm, the first perpendicular magnetization film
up to 25 nm, a Co/Pt multi-layered film of the second perpendicular
magnetization film up to 6 nm, and the carbon film up to 10 nm. As
to the Co/Pt multi-layered film of the second perpendicular
magnetization film, a Co target and a Pt target were alternately
operated to grow a film of 1.5 nm in each part of one cycle, and
thus the total thickness, 6 nm of the second perpendicular
magnetization film was grown in two cycles. Thus, the magnetic
recording medium of which the cross-section is shown in FIG. 2 was
produced. The saturation magnetization of the Co--Cr film formed as
the second underlayer was 25 emu/cc, and the anisotropy energy of
the second perpendicular magnetization film 14 was 2.times.10.sup.7
erg/cc.
[0071] Magnetic recording media of the same structure but having no
second perpendicular magnetization film were produced as samples
for comparison.
[0072] The coercivity (Hc) and read/write characteristics of these
magnetic recording media were evaluated by a vibrating sample
magnetometer (VSM) and a dual head with inductive head for writing
and with magnetoresistive (MR) head for reading. The gap length of
the record head was selected to be 0.2 .mu.m, the shield gap length
of the giant magnetoresistive (GMR) head for reading to be 0.15
.mu.m, and the spacing for measurement to be 0.04 .mu.m. The half
output recording density (D.sub.50) was measure. The signal to
noise ratio, S/N ratio for magnetic recording at 20 kFCI was
measured relative to the S/N ratio of the samples for comparison.
The measured results are shown in Table 2.
2 TABLE 2 EXAMPLES FOR INVENTION COMPARISON FIRST UNDERLAYER Ti-Cr
Ti-Cr SECOND UNDERLAYER CoCr CoCr FIRST PERPENDICULAR FILM CoCrPtTa
CoCrPtTa SECOND PERPENDICULAR FILM Co/Pt No COERCIVITY Hc (kOe) 3.5
2.6 RECORDING DENSITY D.sub.50 (kFCI) 260 190 S/N (RELATIVE VALUE)
2.3 1
[0073] From the table, it was found that the magnetic recording
medium of this embodiment have much larger D.sub.50 and S/N than
the samples for comparison and thus can be used as high-density
magnetic recording media. In addition, a magnetic
recording/reproducing apparatus with GMR head for reading was
produced which employs the 2.5-in diameter magnetic recording
medium made according to this embodiment. This apparatus was
operated under the condition of 8 Gb/in.sup.2 in areal density. The
result was that the error rate can be confined within
1.times.10.sup.-9. Thus, it was confirmed that this apparatus can
be used as ultra-high density magnetic recording/reproducing
apparatus.
[0074] [Embodiment 3]
[0075] A perpendicular magnetization film of Co/Pt multi-layered
film 6 nm thick was provided in place of the second underlayer in
the magnetic recording media of embodiment 2. The other portions
were made the same as above. The produced magnetic recording medium
have the cross-sectional structure shown in FIG. 3. In other words,
on the 2.5-in diameter substrate 11, there were formed in turn the
underlayer 12 of CrTi film 30 nm thick, the perpendicular
magnetization film 33 of Co/Pt multi-layered film 6 nm thick, the
first perpendicular magnetization film 13 of CoCrPtTa film 25 nm
thick, the second perpendicular magnetization film 14 of Co/Pt
multi-layered film 6 nm thick, and the protective film 15 of carbon
film 10 nm thick.
[0076] Magnetic recording media with no second perpendicular
magnetization film of Co/Pt multi-layered film under the protective
film 15 were also produced as samples for comparison.
[0077] As a result of comparing the measurements under the same
read/write conditions as in Embodiment 2, it was confirmed that the
magnetic recording media according to the invention have excellent
D.sub.50 and S/N which are 20%, 75% higher than the samples for
comparison.
[0078] [Embodiment 4]
[0079] The magnetic recording medium having the cross-section shown
in FIG. 4 was produced by depositing on a glass substrate of
2.5-inch diameter according to DC magnetron sputtering method. On
the substrate 11, there were formed in turn the soft magnetic layer
42, the multi-layered perpendicular magnetization film 43, the
first perpendicular magnetization Co-alloy film 13, the second
perpendicular magnetization multi-layered film 43 and the
protective film 15. The soft magnetic layer was deposited by use of
a Fe-80 at % Ni target, the multi-layered perpendicular
magnetization film by a target of Co and Pt, the first
perpendicular magnetization film of Co alloy by a Co-19 at % Cr-8
at % Pt target, the multi-layered second perpendicular
magnetization film by Co, Pt target and the protective film by a
carbon target.
[0080] Under the conditions of a sputtering Ar gas pressure of 3 m
Torr, sputter power of 10 W/cm.sup.2, and substrate temperature of
250.degree. C., a FeNi film was formed up to a thickness of 30 nm,
a Co/Pt multi-layered film of perpendicular magnetization film up
to 6 nm, a CoCrPt perpendicular magnetization film up to 30 nm, a
Co/Pt multi-layered perpendicular magnetization film up to 6 nm,
and the carbon film up to 10 nm. As to the Co/Pt multi-layered
perpendicular magnetization film, a Co target and a Pt target were
alternately operated to grow a film of 1.5 nm in each part of one
cycle, and thus the total thickness, 6 nm of the perpendicular
magnetization film was grown in two cycles. The anisotropy energy
of the Co/Pt multi-layered perpendicular magnetization film was
2.times.10.sup.7 erg/cc.
[0081] Magnetic recording media with no perpendicular magnetization
film of Co/Pt multi-layered film on the medium were also produced
as samples for comparison.
[0082] As a result of comparing the measurements under the same
read/write conditions as in Embodiment 3, it was confirmed that the
magnetic recording medium according to this embodiment have
excellent D.sub.50 and S/N which are 40%, 85% higher than the
samples for comparison and thus can be used as high-density
magnetic recording medium. In addition, a 2.5-in disk type magnetic
recording/reproducing apparatus was produced which has a
high-sensitive read head (see The institute of Electronics and
Communication Engineers of Japan, Technical Journal vol. 96, No.
486, pp. 29 to 35) that makes use of magnetic tunnel phenomenon and
which employs the magnetic recording media produced according to
this embodiment. After the measurement, it was confirmed that under
the condition of area density of 20 Gb/in.sup.2, the apparatus can
attain an error rate of 1.times.10.sup.-9 or below and thus can be
used as ultra-high density recording/reproducing apparatus.
[0083] [Embodiment 5]
[0084] A Co-35 at % Cr film 20 nm thick was provided on the soft
magnetic layer in the magnetic recording medium of embodiment 4.
The other portions were made the same as above. The produced
magnetic recording media have the cross-sectional structure shown
in FIG. 5. In other words, on the 2.5-in diameter substrate 11,
there were formed in turn the soft magnetic layer 42 of Fe--Ni film
30 nm thick, the underlayer 53 of Co--Cr film 20 nm thick, the
first perpendicular magnetization film 13 of Co-19 at % Cr-8 at %
Pt 30 nm thick, the second perpendicular magnetization film 43 of
Co/Pt multi-layered film 6 nm thick, and the protective film 15 of
carbon film 10 nm thick.
[0085] Magnetic recording medium with no perpendicular
magnetization film of Co/Pt multi-layered film under the protective
film were also produced as samples for comparison.
[0086] As a result of comparing the measurements under the same
read/write conditions as in Embodiment 4, it was confirmed that the
magnetic recording medium according to this embodiment have
excellent D.sub.50 and S/N which are 32%, 60% higher than the
samples for comparison.
[0087] [Embodiment 6]
[0088] A Co/Pt multi-layered perpendicular magnetization film 6 nm
thick and a Ti film 20 nm thick were provided on and under the soft
magnetic layer in the magnetic recording medium of embodiment 4.
The other portions were made the same as above. The produced
magnetic recording media have the cross-sectional structure shown
in FIG. 6. In other words, on the 2.5-in diameter substrate 11,
there were formed in turn the underlayer 12 of Ti film 20 nm thick,
the soft magnetic layer 42 of Fe--Ni film 30 nm thick, the Co--Pt
multi-layered perpendicular magnetization film 64 6 nm thick, the
first perpendicular magnetization film 13 of Co-19 at % Cr-8 at %
Pt 30 nm thick, the second perpendicular magnetization film 66 of
Co/Pt multi-layered film 6 nm thick, and the protective film 15 of
carbon film 10 nm thick.
[0089] Magnetic recording medium with no perpendicular
magnetization film of Co/Pt multi-layered film under the protective
film were also produced as samples for comparison. As a result of
comparing the measurements under the same read/write conditions as
in Embodiment 4, it was confirmed that the magnetic recording
medium according to this embodiment have excellent D.sub.50 and S/N
which are 52%, 120% higher than the samples for comparison.
[0090] [Embodiment 7]
[0091] The magnetic recording media having the cross-sectional
structure shown in FIG. 7 were produced by depositing films on the
2.5-in diameter glass substrates according to DC magnetron
sputtering method. On the 2.5-in diameter substrate 11, there were
formed in turn the underlayer 12, the perpendicular magnetization
film 71, the soft magnetic layer 72, and the protective film 15.
The underlayer was grown by use of a Ti-10 at % 5 Cr target, the
perpendicular magnetization film by a Co-19 at % Cr-8 at % Pt
target, the soft magnetic film by a CoNbZr target, and the
protective film by a carbon target. Under the conditions of a
sputtering Ar gas pressure of 3 m Torr, sputter power of 10
W/cm.sup.2, and substrate temperature of 250.degree. C., the CrTi
film was deposited up to a thickness of 30 nm, the first
perpendicular magnetization film up to 30 nm, the soft magnetic
film of CoNbZr up to 4 nm, and the carbon film up to 10 nm.
[0092] In addition, perpendicular magnetic recording medium with
materials Fe--Ni, Fe--Si and Fe--Si--Al used for soft magnetic film
72 were produced. Also, other perpendicular magnetic recording
medium were produced which have films of Co, Ni--Cr having
longitudinal magnetic anisotropy deposited up to a thickness of 4
nm in place of the soft magnetic film 72.
[0093] Perpendicular magnetic recording medium with the carbon
protective film 15 directly formed on the perpendicular
magnetization film 71 were produced as samples for comparison.
[0094] The write/read characteristics of these magnetic recording
medium were measured by the dual head. The gap length of the write
head was selected to be 0.2 mm, the shield gap length of the
magnetoresistive (MR) head for reading to be 0.2 mm, and the
spacing for measurement to be 0.06 mm. The half-output recording
density (D.sub.50) was measured. The noise in the magnetic
recording at 20 kFCI was measured relative to the noise of the
samples for comparison. The measured results are shown in Table
3.
3TABLE 3 EXAMPLES FOR COMPARISON EMBODIMENT 1 UNDERLAYER TiCr TiCr
TiCr TiCr TiCr TiCr TiCr PERPENDICULAR CoCrPt CoCrPt CoCrPt CoCrPt
CoCrPt CoCrPt CoCrPt MAGNETIZATION FILM MAGNETIC FILM No CoNbZr
Fe--Ni Fe--Si Fe--Si--Al Co Ni--Cr RECORDING DENSITY 155 245 220
210 235 240 225 D.sub.50 (kFCI) NOISE 1 0.45 0.52 0.38 0.44 0.50
0.37 (RELATIVE VALUE)
[0095] From the results, it was found that the magnetic recording
media according to this embodiment have much larger D.sub.50 and
lower medium noise than the samples for comparison, and thus can be
used as high-density magnetic recording medium. A 2.5-in disk type
magnetic recording/reproducing apparatus was produced by use of the
magnetic recording medium produced according to this embodiment and
the MR head for reading. It was confirmed that it assures an error
rate of 1.times.10.sup.-9 at a recording density of 6 Gb/in.sup.2,
and thus can be used as an ultra-high density recording/reproducing
apparatus.
[0096] [Embodiment 8]
[0097] The magnetic recording medium having the cross-sectional
structure shown in FIG. 8 were produced by depositing films on the
2.5-in diameter glass substrates according to DC magnetron
sputtering method. On the 2.5-in diameter substrate 11, there were
formed in turn the first underlayer 12, the second underlayer 73,
the perpendicular magnetization film 71, the magnetic film 72, and
the protective film 15. The first underlayer was grown by use of a
Ti-10 at % Cr target, the second underlayer by a Co-35 at % Cr
target, the perpendicular magnetization film by a Co-16 at % Cr-8
at % Pt-3 at % Ta target, the magnetic film by a Fe-80 at % Ni
target, and the protective film by a carbon target. The saturation
magnetization of the Co-35 at % Cr is 20 emu/cc or below, and thus
the second underlayer is a weak ferro magnetic film. Under the
conditions of a sputtering Ar gas pressure of 3 m Torr, sputter
power of 10 W/cm.sup.2, and substrate temperature of 280.degree.
C., the CrTi film was deposited up to a thickness of 30 nm, the
CoCr film up to 15 nm, the perpendicular magnetization film up to
25 nm, the soft magnetic film of FeNi up to 3 nm, and the carbon
film up to 10 nm. The produced perpendicular magnetic recording
media have the cross-sectional structure shown in FIG. 8.
[0098] Perpendicular magnetic recording medium with the carbon
protective film 15 directly formed on the perpendicular
magnetization film 71 were produced as samples for comparison.
[0099] The coercivity (Hc) and write/read characteristics of these
magnetic recording media were evaluated by the vibrating sample
magnetometer (VSM) and the dual head, respectively. The gap length
of the write head was selected to be 0.2 mm, the shield gap length
of the giant magnetoresistive (GMR) head for reading to be 0.15 mm,
and the spacing for measurement to be 0.04 mm. The half-output
recording density (D.sub.50) was measured. The signal to noise
ratio, S/N ratio in the magnetic recording at 20 kFCI was measured
relative to the S/N ratio of the samples for comparison. The
measured results are shown in Table 4.
4 TABLE 4 EXAMPLES EMBOD- FOR IMENT COMPARISON 2 FIRST UNDERLAYER
Ti-Cr Ti-Cr SECOND UNDERLAYER CoCr CoCr PERPENDICULAR MAGNETIZATION
CoCrPtTa CoCrPtTa FILM MAGNETIC FILM No FeNi COERCIVITY Hc (kOe)
2.5 3.1 RECORDING DENSITY D.sub.50 (kFCI) 185 255 S/N (RELATIVE
VALUE) 1 2.3
[0100] From the results, it was found that the perpendicular
magnetic recording media according to this embodiment have much
higher D.sub.50 and S/N than the samples for comparison, and thus
can be used as high-density magnetic recording medium. In addition,
a 2.5-inch disk type magnetic recording/reproducing apparatus was
produced which employs the magnetic recording media made according
to this embodiment and the GMR head for reading. It was confirmed
that this apparatus can attain an error rate of 1.times.10.sup.-9
at a longitudinal recording density of 8 Gb/in.sup.2 and thus can
be used as ultra-high density recording/reproducing apparatus.
[0101] [Embodiment 9]
[0102] The magnetic recording media having the cross-sectional
structure shown in FIG. 9 were produced by depositing films on the
2.5-in diameter glass substrates according to DC magnetron
sputtering method. On the 2.5-in diameter substrate 11, there were
formed in turn the soft magnetic layer 74, the multi-layered
perpendicular magnetization film 75, the magnetic film 72 of CoB
alloy, and the protective film 15. The soft magnetic layer was
grown by use of a Fe-80 at % Ni target, the multi-layered
perpendicular magnetization film by a target of Co and Pt, the
magnetic film of CoB alloy by a Co-6 at % B target, and the
protective film by a carbon target. Under the conditions of a
sputtering Ar gas pressure of 3 m Torr, sputter power of 10
W/cm.sup.2, and substrate temperature of 250.degree. C., the FeNi
film was deposited up to a thickness of 30 nm, the perpendicular
magnetization film of Co/Pt multi-layered film up to 30 nm, the CoB
magnetic film up to 3 nm, and the carbon film up to 10 nm. Here, as
to the Co/Pt multi-layered film as the perpendicular magnetization
film 75, the Co and Pt targets were alternately operated to grow a
film of 1.5-nm thickness in each part of one cycle, and the
perpendicular magnetization film having the total thickness of 30
nm was grown in 10 cycles.
[0103] Perpendicular magnetic recording medium with the carbon
protective film 15 directly formed on the perpendicular
magnetization film 75 were produced as samples for comparison.
[0104] As a result of comparing the write/read characteristics of
these magnetic recording medium in the same way as in Embodiment 8,
it was found that the magnetic recording medium according to this
embodiment have much higher D.sub.50 and S/N than the samples for
comparison, and thus can be used as high-density magnetic recording
media. In addition, a 2.5-in disk type magnetic
recording/reproducing apparatus was produced which has a
high-sensitive read head that makes use of magnetic tunnel
phenomenon and which employs the magnetic recording media produced
according to this embodiment. After the measurement, it was
confirmed that under the condition of area density of 20
Gb/in.sup.2, the apparatus can attain an error rate of
1.times.10.sup.-9 and thus can be used as ultra-high density
recording/reproducing apparatus.
[0105] [Embodiment 10]
[0106] The Co 35 at % Cr film 73 of 20-nm thickness was provided on
the soft magnetic layer 74 in the perpendicular magnetic recording
medium according to Embodiment 9. The other portions were the same
as above. The produced perpendicular magnetic recording media have
the cross-sectional structure shown in FIG. 10. Perpendicular
magnetic recording medium with the carbon protective film 15
directly formed on the perpendicular magnetization film 75 were
produced as samples for comparison. As a result of comparing the
characteristics under the same write/read conditions as in
Embodiment 9, it was confirmed that the perpendicular magnetic
recording medium of the invention have respectively D.sub.50, S/N
25%, 55% improved higher than the samples for comparison.
[0107] [Embodiment 11]
[0108] The present invention will be further described in detail
with reference to FIGS. 11A to 11F.
[0109] In FIGS. 11A to 11F, there is shown a substrate 101 which
was an Si disk with a thermally oxidized Si film formed on the
surface. The substrate may be a glass substrate, NiP coated Al
substrate, carbon substrate or high molecular substrate except the
Si substrate. The rinsed substrates 101 were placed in a sputtering
apparatus, and the apparatus was evacuated up to 1.times.10.sup.-8
Torr. Then, the substrates 101 were heated at 230.degree. C. to
form an underlayer 102 for controlling the crystal grain size and
magnetic anisotropy of the magnetic films. Any type of the
underlayer 102 can be selected depending on the kinds of the
magnetic film to be formed on this underlayer. The magnetic film
can be made of a material of the hexagonal closed packed structure,
body-centered cubic structure, face-centered cubic or rhombic
structure. If the magnetic film is made of a material of hcp
(hexagonal closed packed) structure chiefly containing Co, it is
possible to most generally select for the underlayer a material
chiefly containing an element of Ti, Ta, Ru, Hf, Co of hcp
structure with Cr, V or W added or an amorphous-like material of
Si, Ge or others. Also, the underlayer 102 may be a single-layered
structure of a single material or two or more-layered structure of
different materials. In this embodiment, a Ti-10 at % Cr alloy film
of hcp structure for the first underlayer was deposited on the
substrate 101 up to a thickness of 30 nm, and a non-magnetic alloy
film of Co-35 at % Cr alloy 20 nm thick was formed on the first
underlayer, thus completing the two-layered underlayer 102. The
underlayer 102 has the hcp structure, and its growth orientation
<002> was perpendicular to the substrate surface.
[0110] Then, the magnetic film for recording and protective film
were successively grown on the underlayer in vacuum. For the medium
A of this embodiment according to the invention, as shown in FIG.
11A, a first magnetic thin film 103 of a well magnetically isolated
material was deposited on the underlayer 102, and on this film was
formed a second magnetic film 105 of which the perpendicular
anisotropy constant Ku in the direction perpendicular to the film
surface was larger than the first magnetic layer. The magnetic
films may be made of a material containing chiefly Co, and
additionally at least one of the elements, Cr, Fe, Mo, V, Ta, Pt,
Si, B, Lr, W, Hf, Nb, Ru, Ni and rare earth elements. The first
magnetic films 103 and 105 may have the same or different crystal
structures of thin films. The first magnetic film 103 in the medium
A may be made of a material additionally containing a large amount
of non-magnetic elements of Cr, Mo, V, Ta, Pt, Si, B, Ir, W, Hf,
Nb, Ru, as, for example, Co-17 at % Cr-3 at % Ta alloy or Co-15 at
% Cr-10 at % Pt-3 at % Ta alloy. The first magnetic film is able to
allow the non-magnetic layer or weak ferro magnetic layer locally
segregated within the grain boundaries or grains of the magnetic
crystal grains by the addition of non-magnetic Cr or Ta. By
analyzing the composition on electron microscope, it was confirmed
that the magnetic grains have the effect to improve the magnetic
isolation of magnetic grains. In addition, the magnetic anisotropy
of the magnetic film can be improved by adding Pt. The second
magnetic film 105 in the medium A may be, for example, Co-50 at %
Pt alloy, Co-20 at % Pt-5 at % Cr alloy, or Co-18 at % Pt-10 at %
Cr alloy. The second magnetic film 105 is inferior to the first
magnetic film 103 in the magnetic isolation because it has less
local segregation structure of magnetic layer as compared with the
fist magnetic film, but has a larger magnetic anisotropy constant.
The magnetic anisotropy constant Kua of the first magnetic film 103
of medium A in the direction perpendicular to the film surface was
in the range from 1.times.10.sup.6 erg/cc to 4.times.10.sup.6
erg/cc, while the magnetic anisotropy constant Kub of the second
magnetic film was in the range from 5.times.10.sup.6 erg/cc to
1.times.10.sup.7 erg/cc. If a material having a larger Ku (more
than 1.times.10.sup.7 erg/cc), for example, Pt/Co multi-layered
perpendicular magnetic film or Pd/Co multi-layered perpendicular
magnetic film is used as the second magnetic film, the effect of
the invention can be further improved. The thickness (t1) of the
first magnetic film 103 and that (t2) of the second magnetic film
105 in the medium A according to this embodiment were t1=30 nm, and
t2=20 nm, respectively. If these magnetic film thicknesses satisfy
t1.gtoreq.t2, another combination of thicknesses may be used. On
the second magnetic film was deposited a carbon (c) film 5 nm thick
as the protective film 106.
[0111] A medium B of another embodiment according to the invention
can be constructed as illustrated in FIG. 11B by depositing on the
underlayer 102 the first magnetic film 103 of a material of which
the magnetic isolation is excellent, a non-magnetic intermediate
layer 104, the second magnetic layer 105 of which the perpendicular
magnetic anisotropy constant Ku in the direction perpendicular to
the film surface is large, and then the protective film 106. The
materials and thicknesses of the first and second magnetic films
can be similarly selected as in the medium A. The non-magnetic
intermediate layer 104 in the medium B has the effect of promoting
the epitaxial growth of the second magnetic film 105, the effect of
suppressing the crystal grains of the second magnetic film from
being enlarged, and the effect of controlling the intensity of the
magnetic mutual action between the first and second magnetic films.
The non-magnetic intermediate layer 104 may be made of the same
non-magnetic material as the underlayer 102, and should be
desirably deposited to have a thickness ranging from one atom layer
to 10 nm inclusive. It was 5 nm in this embodiment.
[0112] Samples of five different media for comparison were produced
as shown in FIGS. 11C through 11F. The medium A for comparison, as
shown in FIG. 11C, was constructed by depositing on the substrate
101 the underlayer 102, the magnetic film 103 of a single material
50 nm thick, and the protective layer 105. Here, the magnetic film
was made of the same material as the first magnetic film in medium
A. The medium B for comparison, as shown in FIG. 1D, was
constructed by depositing on the substrate 101 the underlayer 102,
the magnetic film 105 of a single material 50 nm thick, and the
protective layer 106. Here, the magnetic film was made of the same
high Ku material as the second magnetic film in medium A. The
medium C for comparison, as shown in FIG. 11E, was constructed by
depositing on the substrate 101 a lower magnetic film 107, an upper
magnetic layer 108 and then the protective film 106. Here, the
lower magnetic film 107 was made of a material having a low
coercivity (Hc) in the direction perpendicular to the film surface,
for example, 1000 Oe (oersted) or below, or of a material of
CoNiReP or NiP in this embodiment. The upper magnetic film 108 was
made of a material having a larger coercivity (1000 to 1500 Oe) in
the direction perpendicular to the film surface, for example,
CoNiReP, than the lower magnetic film 107. Here, the coercivity of
the thin film was changed by changing the composition of the
material. The medium D for comparison, as shown in FIG. 11F, was
constructed by alternately depositing non-magnetic materials 109
and 110 on the substrate over 50 cycles in a stacked manner. The
non-magnetic material 109 was Pd and deposited 0.4 nm thick as a
layer, and the non-magnetic material 110 was Co-15 at % Cr-3 at %
Ta alloy and deposited 0.2 nm thick as a layer. The magnetic
anisotropy constant Ku of this medium in the direction
perpendicular to the film surface was about 8.times.10.sup.6
erg/cc. The medium E for comparison, as shown in FIG. 11F same as
in the medium D for comparison, was constructed by alternately
depositing the non-magnetic materials 109, 110 on the substrate
over 20 cycles in a stacked manner. The non-magnetic material 109
was Pt and was deposited 1.2 nm thick as a layer, and the magnetic
material 110 was Co and deposited 0.4 nm thick as a layer. The
magnetic anisotropy constant Ku of the medium in the direction
perpendicular to the film surface was about 2.times.10.sup.7
erg/cc.
[0113] Table 5 shows the characteristics of the media of the
embodiment of the invention.
[0114] The values on Table 5 were obtained by using a ring-type
inductive magnetic head (2 .mu.m in track width, 0.2 .mu.m in gap
length) for writing, and a magnetoresistive head (MR head) for
reading and by setting the magnetic spacing (the distance between
the surface of the magnetic film of the medium and the magnetic
pole of the magnetic head) to be 30 nm at the writing/reading
process. In addition, on Table 5, the half-output recording density
D.sub.50 indicates the linear recording density corresponding to
half the reproduced signal output at the low linear recording
density (5 kFCI), and its unit was represented by FCI (Flux Change
per Inch). Also, the noise N/S.sub.0 is the normalized noise, which
noise measured at linear recording density 250 kFCI was normalized
by the reproduced signal output at low linear recording density (5
kFCI). From Table 5, it will be seen that the media A and B of the
invention have an ability of high half-output recording density
(D.sub.50) and low noise characteristic as compared with the
conventional media for comparison, and thus can be satisfactorily
used as media for ultra-high density magnetic recording.
[0115] The magnetized states of the magnetically recorded samples
were observed by a magnetic force microscope (MFM) in order to
compare the causes of the low noise characteristics of media. FIGS.
12A to 12F show the results.
[0116] FIG. 12A shows one example of the magnetized state of media
A, B illustrated in FIGS. 11A and B. The perpendicular magnetic
recording was made by the ring-type inductive magnetic head after
all the media surfaces were erased by DC. As illustrated, a
recorded magnetic domain 132 was recorded on a DC erased region
131. The bright and dark regions respectively indicate different
average orientations of magnetization. As illustrated, clear
recorded magnetic domains 132 were formed in the media A, B of the
invention, and the magnetization transitions 133 had small
instability of which the amplitude was as fine as about 30 nm that
is substantially equivalent to the average diameter of the magnetic
grains of the media. FIG. 12B shows the magnetized state of medium
A for comparison. In this case, by improving the crystal
orientation of magnetic thin films, the fine granulation of
magnetic material and the magnetic isolation of magnetic grains, it
is possible to form clear magnetic domains with small magnetic
transition instability as illustrated in FIG. 12B. However, a large
number of magnetization irreguralities 134 having more than twice
the magnetic crystal grain size appear within the Dc erased region
131 and recorded domains 132 as illustrated. The magnetization
irregularities 134 are called reverse magnetic domains that are
formed in the direction opposite to the magnetizing orientation
chiefly by the effect of demagnetizing field. These magnetization
irregularities 134 cause media noise at the writing/reading
process, and interfere with high-density recording. FIG. 12C shows
the magnetized state of the medium B for comparison. In this case,
the magnetic anisotropy constant of magnetic films was set to be
large, and the mutual action between the magnetic grains is strong.
Thus, a very small number of magnetization irregularities occur,
but the magnetization transition instability is very great as
illustrated. This makes the medium noise increase, and causes a
barrier against the improvement in the recording density. FIG. 12D
shows the magnetized state of medium C for comparison. In this
case, both magnetization transition instability and large-sized
magnetic irregularities occur. FIG. 12E shows the magnetized state
of medium E for comparison. In this case, the perpendicular
magnetic anisotropy constant Ku of the medium is as large as
2.times.10.sup.7 erg/cc, and thus clear magnetic domains with no
magnetic irregularity are formed within the DC erased regions 131
and recorded domains 132. However, the magnetic mutual action
between magnetic grains is strong, and thus the magnetization
transitions 133 have great instability. FIG. 12F shows the
magnetized state of medium D for comparison. In this case, the
magnetization transition instability is small, and clear magnetic
domains can be formed similar to the medium of the invention.
However, the magnetic irregularities 134 appear within the recorded
domains 132 and DC erased regions 131.
[0117] [Embodiment 12]
[0118] One embodiment of magnetic recording apparatus of the
invention will be described with reference to FIGS. 13A and
13B.
[0119] The perpendicular magnetic recording medium produced by way
of experiment and the dual head with inductive head for writing and
with giant magnetoresistive (GMR) head for reading were used to
produce a magnetic recording/reproducing apparatus shown in FIGS.
13A and 13B. Referring to FIGS. 13A and 13B, there are shown a
magnetic recording medium 151, a magnetic recording medium drive
152, a magnetic head 153, a magnetic head drive 154, and a signal
processor 155.
[0120] The magnetic recording medium, or disk 151 was constructed
by depositing on a disk-like substrate such as a glass substrate,
Si substrate, NiP coated aluminum substrate or carbon substrate, an
underlayer for controlling the crystal orientation of a magnetic
film, the magnetic film, and then a protective film. A lubricant
film was further coated on the protective film. The magnetic film
contains chiefly Co, and additionally an element of Cr, Pt, Ti, Ru,
Ta, W, Mo, Pd. The magnetic easy axis of the magnetic film was
oriented in the direction perpendicular to the substrate surface.
In order to obtain the perpendicular recording medium with the
magnetic easy axis of the magnetic film oriented in the direction
perpendicular to the substrate surface, the underlayer for
controlling the structure is made of a material of non-magnetic
CoCr alloy, Ti, TiCr alloy or of a polycrystalline or noncrystal
material with an element of Pt, Ru, Ta, Mo, Pd added to the
non-magnetic alloy to produce hcp structure or an amorphous-like
material of Si, Ge.
[0121] The magnetic head is constructed by a slider, the magnetic
poles of a magnetic write head provided on the slider, and a
magnetoresistive, giant magnetoresistive, spin valve effect or
magnetic tunnel type element for reading. In order to reduce the
magnetization irregularities of the track edges at magnetic writing
process, it is desired to align both track edges of trailing and
leading side magnetic poles of the write head. Since the track
width of the read head is narrower than that of the write head
pole, the read back noise from both written track edges can be
reduced.
[0122] The magnetic head 153 is supported by a suspension 3, and
corrected for the yaw angle caused when the magnetic head is moved
from the inner periphery side of the disk to the outer periphery
side.
[0123] The track width of the write head, the track width of the
GMR head sensor for reading, and the spacing between the head and
the medium were selected to be 0.4 .mu.m, 0.32 .mu.m and 20 nm,
respectively. When the apparatus was operated under the conditions
of PR 5 system signal processing and 36 Gb/in.sup.2 longitudinal
recording density, the error rate was less than
1.times.10.sup.-9.
[0124] Thus, according to the invention, as described above, since
at least two magnetic films of different perpendicular magnetic
anisotropy are formed on the substrate, in which case the
perpendicular magnetic anisotropy of the second magnetic film of
those magnetic films, far from the substrate surface, is selected
to be larger than that of the first magnetic film near to the
substrate surface so as to improve the magnetic isolation of the
first magnetic film near to the substrate surface, or when a
different role is assigned to each magnetic film as they say, the
produced magnetic recording media and magnetic recording apparatus
can be improved in such a manner that the magnetization transition
instability structure and magnetization irregularity structure of
the recorded magnetic domains which cause the medium noise can be
respectively reduced to be small and completely removed to make the
S/N characteristic of the read signal be increased and enough to be
suited for ultra-high area density magnetic recording.
Particularly, it is possible to make high-density magnetic
recording of 5 Gb/in.sup.2 or above, and hence to easily produce
small-size, large-storage-capacity recording apparatus.
* * * * *