U.S. patent application number 11/333381 was filed with the patent office on 2006-06-01 for magnetic recording medium and manufacturing method thereof.
This patent application is currently assigned to Fuji Electric Co., Ltd.. Invention is credited to Yuji Ando, Toyoji Ataka, Ryoichi Kadota, Katsuya Masuda, Satoru Nakamura.
Application Number | 20060115686 11/333381 |
Document ID | / |
Family ID | 29714104 |
Filed Date | 2006-06-01 |
United States Patent
Application |
20060115686 |
Kind Code |
A1 |
Ataka; Toyoji ; et
al. |
June 1, 2006 |
Magnetic recording medium and manufacturing method thereof
Abstract
A high-density magnetic recording medium uses a nonmetallic
substrate, while still providing high in-plane magnetic anisotropy
and remanent coercivity. Such a medium can be formed by depositing
a seed layer on a textured surface of the nonmetallic substrate in
a gas mixture containing oxygen or nitrogen and an inert gas, while
controlling the oxygen concentration or nitrogen concentration, and
subsequently exposing the surface of the seed layer to oxygen or
nitrogen.
Inventors: |
Ataka; Toyoji; (Nagano,
JP) ; Nakamura; Satoru; (Nagano, JP) ; Masuda;
Katsuya; (Nagano, JP) ; Kadota; Ryoichi;
(Nagano, JP) ; Ando; Yuji; (Nagano, JP) |
Correspondence
Address: |
ROSSI, KIMMS & McDOWELL LLP.
P.O. BOX 826
ASHBURN
VA
20146-0826
US
|
Assignee: |
Fuji Electric Co., Ltd.
Kawasaki-ku
JP
|
Family ID: |
29714104 |
Appl. No.: |
11/333381 |
Filed: |
January 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10388366 |
Mar 13, 2003 |
7014882 |
|
|
11333381 |
Jan 17, 2006 |
|
|
|
Current U.S.
Class: |
428/831 ;
204/192.2; 428/831.1; G9B/5.288; G9B/5.299 |
Current CPC
Class: |
G11B 5/7379 20190501;
G11B 5/8404 20130101 |
Class at
Publication: |
428/831 ;
428/831.1; 204/192.2 |
International
Class: |
G11B 5/66 20060101
G11B005/66; C23C 14/00 20060101 C23C014/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 2002 |
JP |
2002-069260 |
Mar 4, 2003 |
JP |
2003-056928 |
Claims
1-10. (canceled)
11. The magnetic recording medium according to claim 18, wherein:
the surface of the seed layer is exposed to gas containing at least
one of oxygen or nitrogen, and the seed layer is composed of Ni--P,
which is deposited on the nonmetallic substrate in a gas mixture
containing oxygen and an inert gas, the concentration of oxygen
being 0.15 to 0.55 vol %.
12. The magnetic recording medium according to claim 11, wherein
the oxygen concentration in the gas mixture, when depositing the
seed layer, is 0.20 to 0.45 vol %.
13. The magnetic recording medium, according to claim 18, wherein:
the surface of the seed layer is exposed to gas containing at least
one of oxygen or nitrogen: and the seed layer is composed of W--Nb,
which is deposited on the nonmetallic substrate in a gas mixture
containing nitrogen and other inert gas, the concentration of
nitrogen being 1.8 to 3.6 vol %.
14. The magnetic recording medium according to claim 13, wherein
the nitrogen concentration in the gas mixture, when depositing the
seed layer, is 1.8 to 2.7 vol %.
15. The magnetic recording medium according to claim 18, wherein:
the surface of the seed layer is exposed to gas containing at least
one of oxygen or nitrogen: and the seed layer is composed of
Ni--Nb, which is deposited on the nonmetallic substrate in a gas
mixture containing nitrogen and other inert gas the concentration
of nitrogen being 0.4 to 3.6 vol %.
16. The magnetic recording medium according to claim 15, wherein
the nitrogen concentration in the gas mixture, when depositing the
seed layer, is 0.4 to 0.9 vol %.
17. The magnetic recording medium according to claim 11, wherein
the magnetic recording medium has an in-plane magnetic anisotropy
of at least 1.50, and a remanent coercivity of at least 3500
Oe.
18. A magnetic recording medium comprising: a nonmetallic substrate
having a textured surface; a seed layer composed of one of Ni--P,
Ni--Nb, or W--Nb formed on the substrate; a nonmagnetic underlayer
formed on the seed layer; and a magnetic layer formed on the
substrate, wherein the magnetic recording medium has an in-plane
magnetic anisotropy of at least 1.30, and a remanent coercivity of
at least 2800 Oe.
19. The magnetic recording medium according to claim 18, wherein
the seed layer is composed of Ni--P and the recording medium has an
in-plane magnetic anisotropy of at least 1.50, and a remanent
coercivity of at least 3500 Oe.
20. The magnetic recording medium according to claim 19, wherein
the magnetic recording medium has an in-plane magnetic anisotropy
of at least 1.60, and a remanent coercivity of at least 3700
Oe.
21. The magnetic recording medium according to claim 18, wherein
the seed layer is composed of W--Nb.
22. The magnetic recording medium according to claim 21, wherein
the magnetic recording medium has an in-plane magnetic anisotropy
of at least 1.40, and a remanent coercivity of at least 3500
Oe.
23. The magnetic recording medium according to claim 18, wherein
the seed layer is composed of Ni--Nb and the recording medium has
an in-plane magnetic anisotropy of at least 1.40, and a remanent
coercivity of at least 3200 Oe.
24. The magnetic recording medium according to claim 23, wherein
the magnetic recording medium has an in-plane magnetic anisotropy
of at least 1.45, and a remanent coercivity of at least 3600
Oe.
25. The magnetic recording medium according to claim 13, wherein
the magnetic recording medium has an in-plane magnetic anisotropy
of at least 1.40, and a remanent coercivity of at least 3500
Oe.
26. The magnetic recording medium according to claim 15, wherein
the magnetic recording medium has an in-plane magnetic anisotropy
of at least 1.40, and a remanent coercivity of at least 3200 Oe.
Description
BACKGROUND
[0001] Conventionally, metal substrates of an aluminum alloy or the
like have been widely used as substrates of magnetic recording
media. These metal substrates are processed to form circular
grooves on their surfaces, which grooves are referred to as a
texture. The texturing on the substrate surface prevents the
magnetic head from contacting the recording medium to prevent wear,
which can happen when the magnetic head flies over the magnetic
recording medium during seeking, and to orient the in-plane
magnetization direction in the circumferential direction, which is
the recording direction. High-density magnetic recording can be
formed with an "anisotropic medium," where magnetic anisotropy is
formed in the medium plane (in-plane magnetic anisotropy). The
output characteristics of the recording medium correspond to the
product of the magnetic layer thickness and the remanent
magnetization (hereinafter described as thickness remanent
magnetization product (Mrt)).
[0002] With a medium having in-plane magnetic anisotropy, where the
output characteristic corresponding to the thickness remanent
magnetization product (Mrt) in the circumferential direction is set
to constant, the remanent magnetization (Mrt) in the
circumferential direction is higher than in the case of an in-plane
isotropic medium. Thus, the magnetic layer can be made thinner and
medium noise caused by the magnetic layer can be reduced. Since the
S/N ratio (signal-to-noise ratio) and so on can be improved, a
high-density recording medium can be obtained. Note that the ratio
between the thickness remanent magnetization product in the
circumferential direction (Mrt(Cir)) and the thickness remanent
magnetization product in the radial direction (Mrt(Rad)), namely
(O.R.-Mrt=Mrt(Cir)/Mrt(Rad)) can be used as an indicator of the
in-plane magnetic anisotropy. The larger O.R.-Mrt, the larger the
in-plane magnetic anisotropy.
[0003] At present, so-called "isotropic media" are the mainstream
magnetic recording media that use a nonmetallic substrate, such as
a glass substrate or a ceramic substrate. But anisotropic magnetic
recording media that use a nonmetallic substrate are being
contemplated. Compared with an anisotropic magnetic recording
medium that uses a metallic substrate, an anisotropic magnetic
recording medium that uses a nonmetallic substrate has better shock
resistance for use in mobile equipment, and higher smoothness for
realizing high-speed rotation for a high-speed server, i.e., higher
rigidity. On the other hand, a magnetic recording medium that uses
a nonmetallic substrate, even if texturing is carried out on the
surface of the nonmetallic substrate, it is difficult to form a
magnetic layer having a sufficient in-plane magnetic anisotropy.
This is due to the thin film crystal orientation and the grain
diameter being different and the thermal expansion of the substrate
being small compared with that of the metallic substrate.
[0004] Obtaining a magnetic recording medium that uses a textured
nonmetallic substrate is difficult as described above, but
proposals to overcome the noted problem have been made. For
instance, Japanese Patent Application Laid-open No. 2001-331934
discloses that by sputtering in oxygen or nitrogen environment to
deposit an orientation adjusting film that adjusts the orientation
of a film immediately thereupon having Ni--P as a principal
component onto a nonmetallic substrate of glass or the like that
has been subjected to texturing, then oxidizing the surface of the
orientation adjusting film, and then depositing a nonmagnetic
underlayer and a magnetic film on the orientation adjusting film
that has been subjected to oxidation treatment without removing the
medium substrate from the film-depositing apparatus, magnetic
anisotropy can be created in the medium plane to obtain a
high-density recording medium using a manufacturing process that is
simpler.
[0005] Recently, however, the recording density of magnetic
recording media has continued to increase at an ever greater rate,
and hence magnetic recording media enabling the realization of yet
higher density magnetic recording are desired. If the magnetic
recording density is increased with an in-plane magnetic recording
medium, the area of the medium per recorded bit becomes smaller,
and hence the playback output drops, and playback becomes
difficult. Although the playback problem can be improved by using a
high-sensitivity head (which increases the playback output), the
medium noise is amplified at the same time to make reading of
recorded information difficult. To make an in-plane magnetic
recording medium have high recording density, it is essential to
reduce the medium noise. Moreover, to win out over the diamagnetic
field from magnetization at bit boundaries and maintain the
magnetization in the recording direction, it is necessary to
increase the remanent coercivity (Hcr), and also reduce the
thickness remanent magnetization product to reduce the diamagnetic
field. The "remanent coercivity (Hcr)" refers to the coercivity in
the remanent curve obtained through measurement of magnetic
relaxation (remanence). If medium noise is reduced by reducing the
thickness of the magnetic layer and decreasing the crystal grain
size of the magnetic layer, the remanent coercivity drops
dramatically and the playback output drops dramatically, and also
the thermal stability of the recording magnetization state becomes
poor so that loss of recorded information becomes problematic. On
the other hand, as described above, by increasing the in-plane
magnetic anisotropy, the medium noise caused by the magnetic layer
can be reduced to improve the S/N ratio. Moreover, a high remanent
coercivity also becomes necessary as one factor for maintaining the
playback output, i.e., improving the thermal stability.
[0006] There is a need for a high-density magnetic recording medium
that uses a nonmetallic substrate having both the high in-plane
magnetic anisotropy and the high remanent coercivity, while
reducing medium noise to improve the S/N ratio. The present
invention addresses this need.
SUMMARY OF THE INVENTION
[0007] The present invention relates to a method of manufacturing a
magnetic recording medium for use in any of various magnetic
recording devices, such as an external storage device for a
computer, and the magnetic recording medium thereof, and the
magnetic recording medium itself.
[0008] One aspect of the present invention is a method of
manufacturing a magnetic recording medium. The method involves
texturing a surface of a nonmetallic substrate, depositing a seed
layer composed of one of Ni--P, Ni--Nb, and W--Nb on the
nonmetallic substrate, exposing the surface of the seed layer to a
gas containing at least one of oxygen or nitrogen, depositing a
nonmagnetic underlayer on the seed layer, and depositing a magnetic
layer on magnetic.
[0009] If the seed layer is composed of Ni--P, the seed layer can
be deposited on the nonmetallic substrate in a gas mixture
containing oxygen and an inert gas, the concentration of oxygen
being 0.15 to 0.55 vol %. More preferably, the oxygen can be 0.20
to 0.45 vol %. The resulting magnetic recording medium can achieve
an in-plane magnetic anisotropy of at least 1.50, and a remanent
coercivity of at least 3500 Oe. More specifically, the magnetic
recording medium can achieve an in-plane magnetic anisotropy of at
least 1.60, and a remanent coercivity of at least 3700 Oe.
[0010] If the seed layer is composed of W--Nb, the seed layer can
be deposited on the nonmetallic substrate in a gas containing a
mixture of nitrogen and other inert gas, the concentration of
nitrogen being 1.8 to 3.6vol %. More perferably, the nitrogen
concentration can be 1.8 to 2.7 vol %. The resulting magnetic
recording medium can achieve an in-plane magnetic anisotropy of at
least 1.30, and a remanent coercivity of at least 2800 Oe. More
specifically, the recording medium can achieve an in-plane magnetic
anisotropy of at least 1.40, and a remanent coercivity of at least
3500 Oe.
[0011] If the seed layer is composed of Ni--Nb, the seed layer can
be deposited on the metallic substrate in a gas mixture containing
nitrogen and other inert gas, the concentration of nitrogen being
0.4 to 3.6 vol %. More preferably, the nitrogen concentration can
0.4 to 0.9 vol %. The resulting magnetic recording medium can
achieve an in-plane magnetic anisotropy of at least 1.40, and a
remanent coercivity of at least 3200 Oe. More specifically, the
magnetic recording medium can achieve an in-plane magnetic
anisotropy of at least 1.45, and a remanent coercivity of at least
3600 Oe.
[0012] Another aspect of the present invention is a magnetic
recording medium made by the above method.
[0013] Another aspect of the present invention is a magnetic
recording medium having the nonmetallic substrate having a textured
surface, the seed layer composed of one of Ni--P, Ni--Nb, and W--Nb
formed on the substrate, the nonmagnetic underlayer formed on the
seed layer; and the magnetic layer formed on the nonmagnetic
underlayer. The magnetic recording medium has an in-plane magnetic
anisotropy and a remanent coercivity as disclosed above
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates an embodiment of a magnetic recording
medium of the present invention.
[0015] FIG. 2 illustrates another embodiment of a magnetic
recording medium of the present invention.
[0016] FIG. 3 illustrates a graph of in-plane magnetic anisotropy
(O.R.-Mrt) versus oxygen concentration of a gas mixture when
depositing a seed layer.
[0017] FIG. 4 illustrates a graph of remanent coercivity (Hcr)
against the oxygen concentration of the gas mixture when depositing
the seed layer.
[0018] FIG. 5 illustrates a graph of thickness remanent
magnetization product (Mrt) against the oxygen concentration of the
gas mixture when depositing the seed layer.
[0019] FIG. 6 illustrates a graph of remanent coercivity squareness
ratio (S') against the oxygen concentration of the gas mixture when
depositing the seed layer.
[0020] FIG. 7, illustrates a graph of an X-ray profile of a
magnetic layer of a magnetic recording medium using an Ni--P seed
layer.
[0021] FIG. 8 illustrates a graph of in-plane magnetic anisotropy
(O.R.-Mrt) versus nitrogen concentration of a gas mixture when
depositing a seed layer.
[0022] FIG. 9 illustrates a graph of remanent coercivity (Hcr)
against the nitrogen concentration of the gas mixture when
depositing the seed layer.
[0023] FIG. 10 illustrates a graph of thickness remanent
magnetization product (Mrt) against the nitrogen concentration of
the gas mixture when depositing the seed layer.
[0024] FIG. 11 illustrates a graph of remanent coercivity
squareness ratio (S') against the nitrogen concentration of the gas
mixture when depositing the seed layer.
[0025] FIG. 12 illustrates a graph of an X-ray profile of a
magnetic layer of a magnetic recording medium using a W--Nb seed
layer.
[0026] FIG. 13 illustrates a graph showing in-plane magnetic
anisotropy (O.R.-Mrt) versus nitrogen concentration of a gas
mixture when depositing a seed layer.
[0027] FIG. 14 illustrates a graph of remanent coercivity (Hcr)
against the nitrogen concentration of the gas mixture when
depositing the seed layer.
[0028] FIG. 15 illustrates a graph of thickness remanent
magnetization product (Mrt) against the nitrogen concentration of
the gas mixture when depositing the seed layer.
[0029] FIG. 16 illustrates a graph of remanent coercivity
squareness ratio (S') against the nitrogen concentration of the gas
mixture when depositing the seed layer.
[0030] FIG. 17 illustrates a graph of an X-ray profile of a
magnetic layer of a magnetic recording medium using an Ni--Nb seed
layer.
DETAILED DESCRIPTION
[0031] FIG. 1 shows one embodiment of a magnetic recording medium
of the present invention. Such a medium has a seed layer 12, a
nonmagnetic underlayer 13, a magnetic layer 14, and a protective
layer 15 formed, in this order, on a nonmetallic substrate 11 with
its surface subjected to texturing. Note that the magnetic
recording medium of the present invention shown in FIG. 1 is merely
an illustrative example of a basic structure. The present invention
is not limited to this particular construction. For example, as
will be described later, an adhesive layer can be provided between
the nonmetallic substrate 11 and the seed layer 12, and an
intermediate layer or the like can be provided between the
nonmagnetic underlayer 13 and the magnetic layer 14.
[0032] The nonmetallic substrate 11 can be substrate made of glass,
monocrystalline silicon, ceramic, polycarbonate, or macromolecular
resin. A glass or ceramic substrate is preferable from the
viewpoint of cost and rigidity.
[0033] Texturing is processing that makes the surface of the
nonmetallic substrate 11 undulating. The texture lines are made
along the circumferential direction. The purpose of carrying out
such texturing on the substrate surface is to orient the in-plane
magnetization direction in the circumferential direction, which is
the recording direction, thus creating magnetic anisotropy in the
medium plane to realize high-density magnetic recording. Texturing
can be carried out, for example, through mechanical polishing or
polishing of the nonmetallic substrate surface using a cloth of
polyester microfibers not containing polishing abrasive grains. To
create the in-plane magnetic anisotropy and to minimize the flying
height of a magnetic head to approximately 8 nm or less, it is
preferable to provide surface roughness Ra of 0.1 to 1 nm, to raise
the in-plane magnetic anisotropy to at least 1.2 nm, and to adjust
the number of grooves formed on the surface to be 20 to 60 per 1 m.
After texturing, it is preferable to further polish or smooth the
surface of the nonmetallic substrate 11, such as tape polishing
using an organic-acid-based washing liquid.
[0034] The seed layer 12 is covers the substrate surface to prevent
alkali metals contained in the glass or the like, which is prone to
corrosion, from leaching out, and to control the in-plane crystal
orientation and control the crystal plane orientation of the
underlayer and the magnetic layer deposited on the seed layer 12.
As the material of the seed layer 12, Ni--P, W--Nb or Ni--Nb can be
used. These materials are preferable because they provide a high
in-plane magnetic anisotropy and a high remanent coercivity when
oxygen or nitrogen concentration of the gas mixture during the
deposition of the seed layer 12 is in a prescribed range. Note that
Ni--P is particularly preferable since in the same Ni--P plating
applied to an ordinary magnetic recording medium Ni--P plating can
be used.
[0035] The above-mentioned Ni--P is preferably Ni.sub.1-xP.sub.x
(at %), where x is 0.15 to 0.35. At less than 0.15, magnetization
will be prone to occurring and hence practical use as a medium will
no longer be possible, whereas at more than 0.35, vaporization of
the P will become very prone to occurring and hence it will become
difficult to produce the target. More preferably, x is 0.18 to
0.27. The above-mentioned W--Nb is preferably W.sub.1-xN.sub.b, (at
%), where x is 0.15 to 0.35. At less than 0.15, the lattice
constant will become too large, which will be unsuitable for
crystal growth of the underlayer 13 and the magnetic layer 14,
whereas at more than 0.35, the target will become expensive due to
being Nb-rich. More preferably, x is 0.2 to 0.3. The
above-mentioned Ni--Nb is preferably Ni.sub.1-xNb.sub.x (at %),
where x is 0.15 to 0.35. At less than 0.15, magnetization will be
prone to occurring and hence practical use as a medium will no
longer be possible, whereas at more than 0.35, the target will
become expensive due to being Nb-rich. More preferably, x is 0.20
to 0.30.
[0036] The seed layer 12 can be deposited using a commonly-used
film deposition method, such as vacuum deposition or sputtering
carried out in a gas mixture of oxygen or nitrogen and an inert
gas, such as argon or helium, after putting the substrate into a
vacuum apparatus and evacuating to a vacuum (preferably less than
1.3.times.10.sup.-5 Pa). By forming the film by deposition in a gas
mixture containing oxygen or nitrogen, the crystal orientation of
the magnetic layer 14 can be improved. If depositing a seed layer
12 comprising Ni--P, the oxygen concentration of the gas mixture of
oxygen and an inert gas is made to be 0.15 to 0.55 vol %,
preferably 0.20 to 0.45 vol %. If depositing a seed layer 12
comprising W--Nb, the nitrogen concentration of the gas mixture of
nitrogen and an inert gas is made to be 1.8 to 3.6 vol %,
preferably 1.8 to 2.7 vol %. If depositing a seed layer 12
comprising Ni--Nb, the nitrogen concentration of the gas mixture of
nitrogen and an inert gas is made to be 0.4 to 3.6 vol %,
preferably 0.4 to 1.8 vol %, more preferably 0.4 to 0.9 vol %. With
the oxygen or nitrogen concentration range as described above, a
high in-plane magnetic anisotropy and a high remanent coercivity
can be obtained.
[0037] The seed layer 12 is preferably deposited while the
substrate temperature is between room temperature (25.degree. C.)
and 300.degree. C., and preferably under pressure between 0.2 and 2
Pa. The thickness of the seed layer 12 is preferably made to be 5
to 20 nm. To secure sufficient surface coverage, it is preferable
for the thickness to be at least 5 nm, whereas if the thickness is
high then the film deposition time takes long. Thus, it is
preferable for the thickness to be not more than 20 nm.
[0038] Gas exposure surface treatment is carried out by exposing
the surface of the seed layer 12 to oxygen or nitrogen. The surface
treatment can be also carried out using a gas mixture of oxygen or
nitrogen and an inert gas, such as argon. The surface treatment is
carried out to control the film plane orientation of the
subsequently formed underlayer 13 and to create a difference in the
crystal strain between the circumferential direction and the radial
direction in the film plane. It is thought that, as a result, the
magnetic layer 14 has anisotropy in the crystal orientation in the
film plane, and hence the medium provides an in-plane magnetic
anisotropy. When carrying out the surface treatment using a gas
mixture of oxygen or nitrogen and an inert gas, to expose the
substrate surface uniformly with the mixed gas, the oxygen or
nitrogen concentration of the gas mixture is preferably 0.5 to 5vol
%, more preferably 1 to 3 vol %. Moreover, to maintain the
uniformity of the in-plane magnetic anisotropy in the magnetic disk
plane, and to increase the remanent coercivity, it is preferable to
carry out the surface treatment for 0.5 to 5 seconds at a pressure
of 0.2 to 2 Pa. Specifically, after depositing the seed layer 12 on
the substrate 11 by sputtering inside a sputtering apparatus
chamber, the surface treatment can be carried out by introducing a
mixed gas of oxygen or nitrogen and an inert gas into the chamber
using gas supply means, thus making the mixed gas come into contact
with the surface of the seed layer 12. After exposing the surface
of the seed layer 12 to the oxygen or nitrogen, texturing can be
further carried out or not carried out on the surface; however, if
texturing is carried out on the surface of the seed layer 12, it is
preferable for the texture lines to run in the circumferential
direction of the substrate, and it is preferable to make the
surface roughness Ra be 0.1 to 1 nm.
[0039] The nonmagnetic underlayer 13 is intended to make the
magnetic particles in the magnetic layer minute and uniform, and to
reduce noise and thus improve the S/N ratio. The nonmagnetic
underlayer 13 can be formed from any commonly-used nonmagnetic
material that is capable of furnishing such a function. For example
Cr, Cr--W, Cr--V, Cr--Mo, Cr--Si, Ni--Al, Mo, W, Pt,
Al.sub.2O.sub.3 or the like can be used. The thickness of the
nonmagnetic underlayer 13 is preferably 0.5 to 20 nm, more
preferably 1.5 to 5 nm. The nonmagnetic underlayer 13 can be a
single-layer film or a multi-layer film, and in the case of a
multi-layer film, the various layers can be of different materials
and thicknesses, or can be of the same material and thickness.
[0040] The nonmagnetic underlayer 13 can be deposited using a
commonly-used film deposition method such as sputtering or vacuum
deposition, and it is preferable to make the substrate temperature
at the film deposition be 150 to 400.degree. C., and the film
deposition pressure be 0.067 to 2 Pa.
[0041] The magnetic layer 14 has a function of recording
information. For the magnetic layer 14, it is preferable to use a
material having Co as the principal component thereof. Co is a
ferromagnetic material that has a close-packed hexagonal (hcp)
structure and uniaxial crystal magnetic anisotropy, and hence is
suitable as the material of the magnetic layer 14. It is preferable
for at least one element selected from Cr, Mo, B, Mn, Ti, W, V, Ta,
Zr, Hf, Cu, Pt, Ru, and Re to be added to the material of the
magnetic layer 14. For making the crystal grains small and
increasing the remanent coercivity and so on, having high quality
(high S/N ratio and sufficient thermal stability) during
high-density recording, and so on, it is preferable to use a
CoCrTa, CoCrPt, CoCrPtB, CoCrPtTa, CoCrPtBCu, or CoCrPtTaB alloy,
with the CoCrPtTa, CoCrPtB, or CoCrPtBCu alloy being particularly
preferable. It is preferable to make the thickness of the magnetic
layer 14 be 10 to 20 nm. It is preferable to make this thickness at
least 10 nm to improve the thermal stability of the recording
magnetization state so that recorded information will not be lost.
On the other hand, it is preferable for this thickness to be not
more than 20 nm to make the crystal grains small and thus decrease
the medium noise and increase the recording density. The thickness
of the magnetic layer 14 is more preferably 14 to 18 nm. The
magnetic layer 14 can be a single-layer film or a multi-layer film.
If a multi-layer film is used, the various layers can be of
different materials and thicknesses, or can be of the same material
and thickness.
[0042] The magnetic layer 14 can be deposited using a commonly-used
film deposition method, such as sputtering or vacuum deposition,
and it is preferable for the substrate to be during the film
deposition to be 150 to 400.degree. C., and the film deposition
pressure to be 0.067 to 1.34 Pa. The surface of the magnetic layer
14 can be subjected to oxidation, nitriding or carbonization
treatment.
[0043] A protective layer 15 can be formed on the magnetic layer 14
as desired. The protective layer 15 has a function of protecting
the magnetic layer that forms the recording layer from impact with
the head, and corrosion due to the corrosivity of the external
environment and so on. Any commonly used material capable of
furnishing such a function can be used. For example carbon,
nitrogen-containing carbon, hydrogen-containing carbon, silicon
oxide or the like can be used. The protective layer 15 can be
formed using a commonly used method, such as sputtering or CVD
(chemical vapor deposition). Moreover, the thickness of the
protective layer 15 is preferably made to be 0.5 to 5 nm. The
protective layer 15 can be a single-layer film or a multi-layer
film.
[0044] FIG. 2 shows another embodiment of a magnetic recording
medium of the present invention. Such an embodiment has an adhesive
layer 22, a seed layer 23, a nonmagnetic underlayer 24, an
intermediate layer 25, a magnetic layer 26, a protective layer 27,
and a lubricating layer 28 formed, in this order, on a. nonmetallic
substrate 21 with its surface subjected to texturing. Note that the
magnetic recording medium shown in FIG. 2 is also merely an
illustrative example of the present invention. Accordingly, the
magnetic recording medium of the present invention is not limited
to this construction.
[0045] In the second embodiment, the nonmetallic substrate 21, the
seed layer 23, the nonmagnetic underlayer 24, the magnetic layer
26, and the protective layer 27 can be formed as described earlier.
The adhesive layer 22, the intermediate layer 25, the protective
layer 27 and the lubricating layer 28 can be provided as desired.
The adhesive layer 22 can be provided between the nonmetallic
substrate 21 and the seed layer 23. The adhesive layer 22 has a
function of preventing the film thereupon (the seed layer 23) from
peeling off the substrate 21. The adhesive layer 22 can be formed
from a material such as Cr, Ti, Ta, W, or an alloy thereof, and can
be deposited using a commonly-used film deposition method, such as
sputtering.
[0046] Moreover, the intermediate layer 25 can be provided between
the nonmagnetic underlayer 24 and the magnetic layer 26. The
intermediate layer 25 has a function of controlling the orientation
of the magnetic layer and suppressing crystal stacking faults. The
intermediate layer 25 can be formed from a material such as CoCr,
CoCrB, CoCrTa, CoCrPtB, CoCrPtTa, or CoCrPtBTa, and can be
deposited using a commonly used film deposition method such as
sputtering.
[0047] Furthermore, the lubricating layer 28 can be provided on the
protective layer 27. The lubricating layer 28 has a function of
improving the function of the head flying over the medium, and
preventing sticking of the head when operation is stopped (with a
drive that does not use an unloading mechanism), and improving the
environment resistance characteristics. The lubricating layer 28
can be a fluorine-type liquid lubricant such as a
perfluoropolyether or the like, and can be formed using a
commonly-used application method or the like.
[0048] The magnetic recording media of the present invention
described above have high in-plane magnetic anisotropy (O.R.--Mrt)
and remanent coercivity. With the magnetic recording medium of the
present invention having a seed layer comprising Ni--P, if the
oxygen concentration of the gas mixture when depositing the seed
layer is 0.15 to 0.55 vol %, the magnetic recording medium of the
present invention provides an O.R.-Mrt of at least 1.50, and a
remanent coercivity of at least 3500 Oe. With the magnetic
recording medium of the present invention having a seed layer
comprising Ni--P, if the in-plane magnetic anisotropy is less than
1.50, then it will not be possible to make the magnetic layer
sufficiently thin, and hence it will not be possible to achieve
high-density recording through reduction of the medium noise. On
the other hand, if the remanent coercivity is less than 3500 Oe,
then the magnetization transition width will become broad and the
S/N ratio will not be improved, and hence it will not be possible
to achieve high-density recording. It is preferable for the oxygen
concentration of the gas mixture when depositing the seed layer to
be 0.20 to 0.45 vol %, for the magnetic recording medium to achieve
an O.R.-Mrt of at least 1.60, and a remanent coercivity of at least
3700 Oe.
[0049] With the magnetic recording medium of the present invention
having a seed layer comprising W--Nb, if the nitrogen concentration
of the gas mixture when depositing the seed layer is 1.8 to 3.6 vol
%, the magnetic recording medium provides an O.R.-Mrt of at least
1.30, and a remanent coercivity of at least 2800 Oe. If the
in-plane magnetic anisotropy is less than 1.30, then it will not be
possible to make the magnetic layer sufficiently thin, and hence it
will not be possible to achieve high-density recording through
reduction of the medium noise. On the other hand, if the remanent
coercivity is less than 2800 Oe, then the magnetization transition
width will become broad and the S/N ratio will not be improved, and
hence it will not be possible to achieve high-density recording. It
is preferable for the nitrogen concentration of the gas mixture
when depositing the seed layer to be 1.8 to 2.7 vol %, and for the
magnetic recording medium to achieve an O.R.-Mrt of at least 1.40,
and a remanent coercivity of at least 3500 Oe.
[0050] With the magnetic recording medium of the present invention
having a seed layer comprising Ni--Nb, if the nitrogen
concentration of the gas mixture when depositing the seed layer is
0.4 to 3.6 vol %, the magnetic recording medium provides an
O.R.-Mrt of at least 1.40, and a remanent coercivity of at least
3200 Oe. If the in-plane magnetic anisotropy is less than 1.40,
then it will not be possible to make the magnetic layer
sufficiently thin, and hence it will not be possible to achieve
high-density recording through reduction of the medium noise. On
the other hand, if the remanent coercivity is less than 3200 Oe,
then the magnetization transition width will become broad and the
S/N ratio will not be improved, and hence it will not be possible
to achieve high-density recording. Furthermore, if the nitrogen
concentration of the gas mixture when depositing the seed layer is
0.4 to 0.9 vol %, the magnetic recording medium achieves an
O.R.-Mrt of at least 1.45, and a remanent coercivity of at least
3600 Oe.
[0051] Following is a description of the present invention through
examples; however, the scope of the present invention is not
limited to these examples.
[0052] In the first example, referring to FIG. 2, a magnetic
recording medium was manufactured in which an adhesive layer, a
seed layer comprising Ni--P, a nonmagnetic underlayer, an
intermediate layer, a magnetic layer, and a protective layer were
formed in this order on a glass substrate with its surface
subjected to texturing. Following is a detailed description of the
method of manufacturing the magnetic recording medium.
[0053] Texturing was carried out in the circumferential direction
on a surface of a glass substrate (N5 substrate made by Hoya) as a
nonmetallic substrate. Specifically, polishing was carried out on
the surface of the glass substrate, thus adjusting the surface
roughness Ra to 0.35 nm as measured using an AFM on a 30
.mu.m-square area of the substrate surface, and the number of
grooves formed on the substrate surface to 35 per .mu.m as measured
using an AFM on a 1 .mu.m-square area of the substrate surface.
[0054] Regarding the polishing, the substrate was chucked onto a
spindle and rotated at 300 rpm, and while feeding in a woven cloth
of polyester microfibers (fiber diameter 1.5 .mu.m) not containing
polishing abrasive grains at 60 mm/min, the cloth was pushed
against the substrate with a pushing pressure of 78.4 kPa (0.8
kgf/cm.sup.2) via a pushing member of rubber hardness (according to
IRHD pocket hardness test for spring-type medium hardness described
in JIS K6253) 60.degree. for 25 seconds while dripping a slurry
containing 0.5 to 1 mass % of diamond abrasive grains of mean
particle diameter 0.05 to 0.1 .mu.m.
[0055] Next, the substrate was chucked onto a spindle and rotated
at 300 rpm, and while feeding in a woven cloth of polyester
microfibers (fiber diameter 1.5 .mu.m) not containing polishing
abrasive grains at 20 mm/min, the cloth was pushed against the
substrate with a pushing pressure of 78.4 kPa (0.8 kgf/cm.sup.2)
via a pushing member of rubber hardness 60.degree. for 25 seconds
while dripping a washing liquid containing an organic-acid-type
solvent but not containing abrasive grains.
[0056] After the washing, the substrate was put into a DC
sputtering apparatus, and after evacuating to a vacuum, an adhesive
layer comprising Cr was deposited with a substrate temperature at
the film deposition of 25.degree. C. and a film deposition pressure
of 0.4 Pa. The thickness of the adhesive layer was made to be 1.2
nm.
[0057] Next, a seed layer comprising Ni--P20(Ni.sub.0.8P.sub.0.2)
was deposited with a substrate temperature at the film deposition
of 25.degree. C. and a film deposition pressure of 1.3 Pa in a gas
mixture of oxygen and argon. The oxygen concentration was 0.4 vol
%. The thickness of the seed layer was made to be 20 nm.
[0058] Next, the surface of the seed layer was subjected to gas
exposure for 5 seconds at gas flow rate of 30 cc/min using a gas
mixture of oxygen (concentration of 2 vol %) and argon.
[0059] A nonmagnetic underlayer comprising Cr of thickness 2.3 nm
was deposited by sputtering with a substrate temperature at the
film deposition of 300.degree. C. and a film deposition pressure of
0.4 Pa, an intermediate layer comprising CoCr of thickness 1 nm was
deposited by sputtering on the nonmagnetic underlayer with a
substrate temperature at the film deposition of 300.degree. C. and
a film deposition pressure of 0.4Pa, a magnetic layer comprising
CoCrPtB of thickness 16.3 to 17 nm was deposited by sputtering on
the intermediate layer with a substrate temperature at the film
deposition of 300.degree. C. and a film deposition pressure of 1
Pa, and then a carbon protective layer of thickness 5 nm was
formed.
[0060] FIGS. 3 to 6 show magnetic characteristics of magnetic
recording media obtained as described above, except that the oxygen
concentration of the gas mixture was varied from 0 to 1.4 vol %.
FIGS. 3, 4, 5, and 6 are graphs showing respectively the in-plane
magnetic anisotropy (O.R.-Mrt), the thickness remanent
magnetization product (Mrt), the remanent coercivity (Hcr), and the
squareness ratio (the remanent coercivity squareness ratio S'),
versus the oxygen concentration of the gas mixture when depositing
the seed layer of magnetic recording media obtained as described
above. When the oxygen concentration of the gas mixture when
depositing the seed layer was 0.15 to 0.55 vol %, the O.R.-Mrt, the
remanent coercivity (Hcr), the thickness remanent magnetization
product (Mrt), and the squareness ratio (S') exhibited high values
of at least 1.5, at least 3500 Oe, at least 0.35 memu/cm.sup.2, and
at least 0.7 respectively. When the oxygen concentration of the gas
mixture when depositing the seed layer was 0.20 to 0.45 vol %, the
O.R.-Mrt, the remanent coercivity (Hcr), the thickness remanent
magnetization product (Mrt), and the squareness ratio (S')
exhibited high values of at least 1.60, at least 3700 Oe, at least
0.35 memu/cm.sup.2, and at least 0.75 respectively. At an oxygen
concentration of 0.35 vol %, highly desirable values were
exhibited, namely an O.R.-Mrt of 1.66, a remanent coercivity of
3814 Oe, a medium noise of 10.9, and an S/N ratio of 14.9.
[0061] FIG. 7 shows the results of structural analysis using X-ray
diffraction by the .theta.-2.theta. method on the magnetic layer of
magnetic recording media obtained as described above. The peak of
Co(110) at d=1.287(2.theta.=73.5.degree.) was detected with an
oxygen concentration of 0.35 vol % when depositing the seed layer,
but was not detected when the oxygen concentration was 1.4 vol %.
This corresponds to the O.R.-Mrt becoming high where the Co(110)
peak intensity is strong.
[0062] In the second example, referring to FIG. 2, a magnetic
recording medium was manufactured in which an adhesive layer, a
seed layer comprising W--Nb, a nonmagnetic underlayer, an
intermediate layer, a magnetic layer, and a protective layer were
formed in this order on a glass substrate with its surface
subjected to texturing. Following is a detailed description of the
method of manufacturing the magnetic recording medium.
[0063] As in the first example, texturing was carried out in the
circumferential direction on a surface of a glass substrate (N5
substrate made by Hoya) as a nonmetallic substrate. Specifically,
polishing was carried out on the surface of the glass substrate,
thus adjusting the surface roughness Ra to 0.35 nm as measured
using an AFM on a 30 .mu.m-square area of the substrate surface,
and the number of grooves formed on the substrate surface to 35 per
.mu.m as measured using an AFM on a 1 .mu.m-square area of the
substrate surface.
[0064] Regarding the polishing, the substrate was chucked onto a
spindle and rotated at 300 rpm, and while feeding in a woven cloth
of polyester microfibers (fiber diameter 1.5 .mu.m) not containing
polishing abrasive grains at 60 mm/min, the cloth was pushed
against the substrate with a pushing pressure of 78.4 kPa (0.8
kgf/cm.sup.2) via a pushing member of rubber hardness (according to
IRHD pocket hardness test for spring-type medium hardness described
in JIS K6253) 60.degree. for 25 seconds while dripping a slurry
containing 0.5 to 1 mass % of diamond abrasive grains of mean
particle diameter 0.05 to 0.1 .mu.m.
[0065] Next, the substrate was chucked onto a spindle and rotated
at 300 rpm, and while feeding in a woven cloth of polyester
microfibers (fiber diameter 1.5 .mu.m) not containing polishing
abrasive grains at 20 mm/min, the cloth was pushed against the
substrate with a pushing pressure of 78.4 kPa (0.8 kgf/cm.sup.2)
via a pushing member of rubber hardness 60.degree. for 25 seconds
while dripping a washing liquid containing an organic-acid-type
solvent but not containing abrasive grains.
[0066] After the washing, the substrate was put into a DC
sputtering apparatus, and after evacuating to a vacuum, an adhesive
layer comprising Cr was deposited with a substrate temperature at
the film deposition of 25.degree. C. and a film deposition pressure
of 0.4 Pa. The thickness of the adhesive layer was made to be 1
nm.
[0067] Next, a seed layer comprising W--Nb25(W.sub.0.75Nb.sub.0.25)
was deposited with a substrate temperature at the film deposition
of 25.degree. C. and a film deposition pressure of 1.3 Pa in a gas
mixture of nitrogen (concentration of 1.8 vol5) and argon. The
thickness of the seed layer was made to be 20 nm.
[0068] Next, the surface of the seed layer was subjected to gas
exposure for 5 seconds at gas flow rate of 30 cc/min using a mixed
gas of oxygen (concentration of 2 vol %) and argon.
[0069] A nonmagnetic underlayer comprising Cr of thickness 2.3 nm
was deposited by sputtering with a substrate temperature at the
film deposition of 300.degree. C. and a film deposition pressure of
0.4 Pa, an intermediate layer comprising CoCr of thickness 1 nm was
deposited by sputtering on the nonmagnetic underlayer with a
substrate temperature at the film deposition of 300.degree. C. and
a film deposition pressure of 0.4 Pa, a magnetic layer comprising
CoCrPtB of thickness 16.3nm was deposited by sputtering on the
intermediate layer with a substrate temperature at the film
deposition of 300.degree. C. and a film deposition pressure of 1
Pa, and then a carbon protective layer of thickness 5 nm was
formed.
[0070] FIGS. 8 to 11 show magnetic characteristics of magnetic
recording media obtained as described above in the second example,
except that the oxygen concentration of the gas mixture was varied
from 0 to 3.6 vol %. FIGS. 8, 9, 10 and 11 are graphs showing
respectively the in-plane magnetic anisotropy (O.R.-Mrt), the
remanent coercivity (Hcr), the thickness remanent magnetization
product (Mrt), and the squareness ratio (the remanent coercivity
squareness ratio S'), versus the nitrogen concentration of the gas
mixture when depositing the seed layer of magnetic recording media
obtained as described above. When the nitrogen concentration of the
gas mixture when depositing the seed layer was 1.8 to 3.6 vol %,
the O.R.-Mrt, the remanent coercivity (Hcr), the thickness remanent
magnetization product (Mrt), and the squareness ratio (S')
exhibited high values of at least 1.30, at least 2800 Oe, at least
0.35 memu/cm.sup.2, and at least 0.7 respectively. When the
nitrogen concentration of the gas mixture when depositing the seed
layer was 1.8 to 2.7 vol %, the O.R.-Mrt, the remanent coercivity
(Hcr), the thickness remanent magnetization product (Mrt), and the
squareness ratio (S') exhibited high values of at least 1.40, at
least 3500 Oe, at least 0.35 memu/cm.sup.2, and at least 0.70
respectively. At a nitrogen concentration of the gas mixture when
depositing the seed layer of 1.8 vol %, highly desirable values
were exhibited, namely an O.R.-Mrt of 1.42, a medium noise of 11.3,
a remanent coercivity of 3700 Oe, and an S/N ratio of 13.6. A
highly favorable medium noise and S/N ratio were also obtained at
nitrogen concentrations of 2.7 vol % and 3.6 vol % (Table 2).
[0071] FIG. 12 shows the results of structural analysis using X-ray
diffraction by the .theta.-2.theta. method on the magnetic layer of
magnetic recording media obtained as described above with respect
to the second example. When gas doping was not carried out when
depositing the seed layer, a peak appeared clearly close to
d=2.249(2.theta.=40.1.degree.). A similar peak was detected even
with a nitrogen concentration of 0.35 vol %, but was not detected
when the nitrogen concentration was 1.8 to 3.6 vol %. However, when
the nitrogen concentration was 1.8 to 3.6 vol %, a Co(110) peak
appeared clearly close to d=1.287(2.theta.=73.5.degree.). This
corresponds to the O.R.-Mrt becoming high where the Co(110) peak
intensity is strong.
[0072] In the third example, referring to FIG. 3, a magnetic
recording medium was manufactured in which an adhesive layer, a
seed layer comprising Ni--Nb, a nonmagnetic underlayer, an
intermediate layer, a magnetic layer, and a protective layer were
formed, in this order, on a glass substrate with its surface
subjected to texturing. Following is a detailed description of the
method of manufacturing the magnetic recording medium according to
the third example.
[0073] As in the first and second examples, texturing was carried
out in the circumferential direction on a surface of a glass
substrate (N5 substrate made by Hoya) as a nonmetallic substrate.
Specifically, polishing was carried out on the surface of the glass
substrate, thus adjusting the surface roughness Ra to 0.35 nm as
measured using an AFM on a 30 .mu.m-square area of the substrate
surface, and the number of grooves formed on the substrate surface
to 35 per gm as measured using an AFM on a 1 .mu.m-square area of
the substrate surface.
[0074] Regarding the polishing, the substrate was chucked onto a
spindle and rotated at 300 rpm, and while feeding in a woven cloth
of polyester microfibers (fiber diameter 1.5 .mu.m) not containing
polishing abrasive grains at 60 mm/min, the cloth was pushed
against the substrate with a pushing pressure of 78.4 kPa (0.8
kgf/cm.sup.2) via a pushing member of rubber hardness (according to
IRHD pocket hardness test for spring-type medium hardness described
in JIS K6253) 60.degree. for 25 seconds while dripping a slurry
containing 0.5 to 1mass % of diamond abrasive grains of mean
particle diameter 0.05 to 0.1 .mu.m.
[0075] Next, the substrate was chucked onto a spindle and rotated
at 300 rpm, and while feeding in a woven cloth of polyester
microfibers (fiber diameter 1.5 .mu.m) not containing polishing
abrasive grains at 20 mm/min, the cloth was pushed against the
substrate with a pushing pressure of 78.4 kPa (0.8 kgf/cm.sup.2)
via a pushing member of rubber hardness 60.degree. for 25 seconds
while dripping a washing liquid containing an organic-acid-type
solvent but not containing abrasive grains.
[0076] After the washing, the substrate was put into a DC
sputtering apparatus, and after evacuating to a vacuum, an adhesive
layer comprising Cr was deposited with a substrate temperature at
the film deposition of 25.degree. C. and a film deposition pressure
of 0.4 Pa. The thickness of the adhesive layer was made to be 1
nm.
[0077] Next, a seed layer comprising Ni--Nb30(Ni.sub.0.7Nb.sub.0.3)
was deposited with a substrate temperature at the film deposition
of 25.degree. C. and a film deposition pressure of 1.3 Pa in a gas
mixture of nitrogen (concentration of 0 to 3/6 vol %) and argon.
The thickness of the seed layer was made to be 20 nm.
[0078] Next, the surface of the seed layer was subjected to gas
exposure for 5 seconds at gas flow rate of 30 cc/min using a mixed
gas of oxygen (concentration of 2 vol %) and argon.
[0079] A nonmagnetic underlayer comprising Cr of thickness 2.3 nm
was deposited by sputtering with a substrate temperature at the
film deposition of 300.degree. C. and a film deposition pressure of
0.4 Pa, an intermediate layer comprising CoCr of thickness 0.8 nm
was deposited by sputtering on the nonmagnetic underlayer with a
substrate temperature at the film deposition of 300.degree. C. and
a film deposition pressure of 0.4 Pa, a magnetic layer comprising
CoCrPtB of thickness 16.5 nm was deposited by sputtering on the
intermediate layer with a substrate temperature at the film
deposition of 300.degree. C. and a film deposition pressure of 1
Pa, and then a carbon protective layer of thickness 5 nm was
formed.
[0080] FIGS. 13, 14, 15 and 16 are graphs showing respectively the
in-plane magnetic anisotropy (O.R.-Mrt), the remanent coercivity
(Hcr), the thickness remanent magnetization product (Mrt), and the
squareness ratio (the remanent coercivity squareness ratio S'),
versus the nitrogen concentration of the gas mixture when
depositing the seed layer of magnetic recording media obtained as
described above. When the nitrogen concentration of the gas mixture
when depositing the seed layer was 0.4 to 3.6 vol %, the O.R.-Mrt,
the remanent coercivity (Hcr), the thickness remanent magnetization
product (Mrt), and the squareness ratio (S') exhibited high values
of at least 1.40, at least 3200 Oe, at least 0.35 memu/cm.sup.2,
and at least 0.7 respectively. When the nitrogen concentration of
the mixed gas when depositing the seed layer was 0.4 to 1.8 vol %,
the O.R.-Mrt, the remanent coercivity (Hcr), the thickness remanent
magnetization product (Mrt), and the squareness ratio (S')
exhibited high values of at least 1.45, at least 3400 Oe, at least
0.37 memu/cm.sup.2, and at least 0.75 respectively. In the case
that the nitrogen concentration of the gas mixture when depositing
the seed layer was 0.4 to 0.9 vol %, the O.R.-Mrt, the remanent
coercivity (Hcr), the thickness remanent magnetization product
(Mrt), and the squareness ratio (S') exhibited high values of at
least 1.45, at least 3600 Oe, at least 0.38 memu/cm.sup.2, and at
least 0.75 respectively. At a nitrogen concentration of the gas
mixture when depositing the seed layer of 0.4 vol %, the values
exhibited were an O.R.-Mrt of 1.49, a remanent coercivity of 3750
Oe, a medium noise of 15.0, and an S/N ratio of 11.4.
[0081] FIG. 17 shows the results of structural analysis using X-ray
diffraction by the .theta.-2.theta. method on the magnetic layer of
magnetic recording media obtained as described above. When gas
doping was not carried out when depositing the seed layer, peaks
were not formed. At a nitrogen concentration of 0.35 vol %, a
Co(110) peak appeared clearly close to
d=1.287(2.theta.=73.5.degree.). Furthermore, at a nitrogen
concentration of 1.8 vol %, peaks were not detected. This
corresponds to the O.R.-Mrt becoming high where the Co(110) peak
intensity is strong.
[0082] The manufacturing conditions, magnetic characteristics and
read and write characteristics for the magnetic recording media
obtained as described above are collected together in Table 1 and
2. Table 1 and 2 shows the following measurement values: [0083]
TAA: The mean value over one cycle of the amplitude of the envelope
waveform (units: .mu.Vp-p) [0084] TAA-LF: TAA in the case that the
writing frequency is low [0085] TAA-MF: TAA in the case that the
writing frequency is medium [0086] TAA-1.5T: TAA in the case that
the writing frequency is high [0087] Resolution: The percentage
ratio of TAA-MF to TAA-LF. [0088] O/W: After recording an LF
signal, twenty times the log of the ratio of the LF playback output
between after and before overwriting when an MF signal is
overwritten (units: -dB); namely O/W=20 log[(LF playback output
after MF overwriting)/(LF playback output before MF overwriting)].
[0089] PW50: Half width of playback waveform during solitary wave
signal recording (units: nm) [0090] Medium noise:The square root of
the value obtained by subtracting the square of the integral noise
caused by the head (Nh) and the square of the integral noise caused
by the circuit (Nc) from the square of the integral noise of the
playback waveform during 1.5T signal recording (Nt); namely Nm=
4(Nt.sup.2-Nh.sup.2-Nc.sup.2). [0091] S/N ratio: twenty times the
log of the ratio of TM during 1.5T signal recording (.mu.Vp-p) and
two times the medium noise (Nm (iV)) (dB);namely SNR=20 log
(TAA--1.5T/2Nm)
[0092] The magnetic characteristics, i.e., the in-plane magnetic
anisotropy (O.R.-Mrt), the remanent coercivity (Hcr), the thickness
remanent magnetization product (Mrt), and the squareness ratio (S')
were obtained by taking measurements at the two points 0.degree.
and 180.degree. with a radius of r=22 mm using an ORM measuring
device (made by Innovated Instruments), and then taking the
mean.
[0093] For KuV/k.sub.BT, Hcr was measured with the magnetic field
holding time being changed (1 to 100 s). It was obtained from
Hc(t)=H.sub.0{1-[(k.sub.BT/KuV)In(At)].sup.n}}. M. P. Sharrock,
Time dependence of switching field in magnetic recording media,
Journal of Applied Physics, Vol. 76 (1994), 6413-6418 was referred
to.
[0094] For the electromagnetic conversion characteristics, an RW
tester (made by Guzik; RWA-2585PRML, ANA985PRML, S-1701A) was used.
A 40 Gbit/inch head was used as the magnetic head. TABLE-US-00001
TABLE 1 Sputtering Conditions Seed Thickness of Magnetic
Characteristics Layer Deposition Magnetic Layer KuV/k Example
Material Gas (nm) Hcr Mrt S' O.R. - Mrt BT 1 Ni--P20 Ar-0.35%
O.sub.2 17.0 3814 0.41 0.78 1.66 68 2 Ni--P20 Ar 16.3 3950 0.40
0.83 1.39 78 3 W--Nb25 Ar-1.8% N.sub.2 16.3 3700 0.35 0.71 1.42 70
4 W--Nb25 Ar-2.7% N.sub.2 16.3 3500 0.35 0.71 1.42 5 W--Nb25
Ar-3.6% N.sub.2 16.3 2850 0.36 0.74 1.33 6 Ni--Nb30 Ar-0.4% N.sub.2
16.5 3750 0.41 0.85 1.49 76
[0095] TABLE-US-00002 TABLE 2 Measurement Radius Rotational Speed
Read & Write Characteristics Measurement (mm) (rpm) Track
Recording TAA Output Point 22.8 10,000 Density (kFCl) (.mu.Vp-p)
Resolution MD Pw50 Medium 400.2 Example LF MF 1.5 T (%) OW (-dB)
(nm) Noise S/N Ratio (dB) 1 743 541 377 72.8 28.1 106.9 10.9 14.9 2
713 511 358 71.7 28.6 109.8 14.7 11.8 3 700 492 338 70.3 28.4 110.6
11.3 13.6 4 698 489 333 70.0 25.8 111.0 10.9 13.7 5 702 488 333
69.3 27.6 110.8 11.0 13.7 6 718 509 355 71.0 29.7 110.2 15.0
11.4
[0096] As described above, according to the present invention, a
magnetic recording medium that has a high in-plane magnetic
anisotropy and a high remanent coercivity and hence is suitable for
increasing recording density can be obtained.
[0097] Given the disclosure of the present invention, one versed in
the art would appreciate that there may be other embodiments and
modifications within the scope and spirit of the present invention.
Accordingly, all modifications and equivalents attainable by one
versed in the art from the present disclosure within the scope and
spirit of the present invention are to be included as further
embodiments of the present invention. The scope of the present
invention accordingly is to be defined as set forth in the appended
claims.
[0098] The disclosure of the priority application, JP PA
2002-069260, in its entirety, including the drawings, claims, and
the specification thereof, is incorporated herein by reference.
* * * * *