Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-08-09
2003-12-30
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S611000, C428S666000, C428S900000
Reexamination Certificate
active
06670055
ABSTRACT:
REFERENCE TO RELATED APPLICATION
This application claims the priority right under Paris Convention of Japanese Patent Application No. 2000-245977 filed on Aug. 14, 2000, the entire disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to magnetic recording media such as hard disks incorporated in external storage devices of computers, particularly to magnetic recording media with high coersive force and low noise in which a pre-coat layer for decrease in size of crystal grains of an underlayer and a magnetic layer and for suppressing dispersion of grain size of an underlayer and a magnetic layer is provided between a substrate and the underlayer, and manufacturing methods thereof.
(ii) Description of the Related Art
As a magnetic recording medium of this kind, for example, a magnetic recording medium as described in the specification of Japanese Patent Application No. 11-094391, which is a prior application of the present applicant, has been proposed. This magnetic recording medium is constructed by sequentially laminating, on a substrate, a seed layer in which an intermediate layer is interposed between at least two or more layers of non-magnetic films, a Cr or Cr-alloy underlayer, a Co-alloy magnetic layer, and attains high coersive force and low noise.
The high coersive force of this magnetic recording medium is attained by the manner that the seed layer enhances the crystal orientation of (110) plane in the body center cubic (bcc) of the Cr or Cr-alloy as the underlayer, and the crystal orientation of (100) plane in which the magnetization easy axis (c axis) of the Co magnetic layer epitaxial-grown thereon becomes parallel in plane is improved.
Besides, in this magnetic recording medium, since the film thickness of the underlayer can be thinned by providing the seed layer, by thinning the underlayer, Co magnetic grains thereon are made fine, and since the magnetization transition region (magnetic wall width) between recording bits can be decreased, noise can be reduced.
SUMMARY OF THE INVENTION
In recent years, development of magnetic recording media in which noise is reduced attendant upon still higher recording density of magnetic recording media and S/N ratio is improved is desired.
Although the crystal grain diameter of the magnetic layer must be decreased as fine as possible, if the crystal grain diameter of the magnetic layer is made very fine, there is a problem that a phenomenon in which the magnetization becomes thermally unstable, the recorded signal is attenuated with time, and finally the recorded signal disappears, that is, a phenomenon called thermal fluctuation occurs. Noise and thermal fluctuation are in relation of trade-off, and as the crystal grain diameter of the magnetic layer is decreased, although noise is reduced, the signal attenuation by the thermal fluctuation becomes large, and the recorded signal becomes easy to be attenuated with time or disappear. If the thermal fluctuation occurs, other than the signal attenuation (reduction of reproduction output), medium noise increases and the value of PW50 value (half pulse width of isolated reproduction signal) is deteriorated.
As a fine structure of a medium desired for high-density recording, it has become impossible that, as well as decreasing the crystal grains of the magnetic layer, the dispersion of grain size (grain diameter distribution) is decreased and generation of excessively fine grains apt to receive influence of thermal fluctuation is suppressed.
Because the crystal structure of the magnetic layer is obtained by taking over the crystal structure of the underlayer, as well as making the crystal grains of the underlayer still finer, the grain diameter distribution must be made small.
The present inventor and so on have made the present invention as a result of repeating earnest examination based on knowledge whether or not decrease in crystal grain of the magnetic layer and improvement of the dispersion of grain size can be intended by interposing a pre-coat layer between a substrate and the underlayer.
Accordingly, it is an object of the present invention to provide magnetic recording media with high coersive force, hard to receive the influence of thermal fluctuation, and bringing about considerable improvement of S/N ratio.
The present invention has the following constitutions.
Constitution 1
A magnetic recording medium in which at least an underlayer and a magnetic layer are sequentially formed on a substrate, wherein a pre-coat layer for decrease in size of crystal grains of the underlayer and magnetic layer and for suppressing dispersion of grain size of the underlayer and magnetic layer is interposed between said substrate and the underlayer, and in said pre-coat layer, a lower layer containing Ni and P and an upper layer made of a Cr alloy are sequentially laminated from said substrate side.
Constitution 2
The magnetic recording medium according to construction 1, wherein the crystal structure of said pre-coat layer is an amorphous structure or an almost amorphous structure.
Constitution 3
The magnetic recording medium according to constitution 1 or 2, wherein said pre-coat layer contains nitrogen.
Constitution 4
The magnetic recording medium according to constitution 3, wherein said nitrogen is contained at 1 to 20 at %.
Constitution 5
The magnetic recording medium according to any one of constitutions 1 to 4, wherein said upper layer is a Cr alloy containing Cr and one of Zr and W.
Constitution 6
The magnetic recording medium according to any one of constitutions 1 to 5, wherein a seed layer for controlling the crystal grain diameter of the underlayer and magnetic layer is formed between said pre-coat layer and the underlayer.
Constitution 7
The magnetic recording medium according to any one of constitutions 1 to 6, wherein the film thickness of said lower layer is 50 to 2000 Å.
Constitution 8
The magnetic recording medium according to any one of constitutions 1 to 7, wherein the film thickness of said upper layer is 5 to 300 Å.
Constitution 9
The magnetic recording medium according to any one of constitutions 1 to 8, wherein said substrate is a glass substrate.
Constitution 10
The magnetic recording medium according to any one of constitutions 1 to 9, wherein said magnetic recording medium is used under conditions of a linear recording density of 300 kfci or more.
Constitution 11
A manufacturing method of a magnetic recording medium made by sequentially forming at least an underlayer and a magnetic layer on a substrate by sputtering, wherein a pre-coat layer having a lower layer containing Ni and P and an upper layer made of a Cr alloy is sequentially formed by sputtering between said substrate and the underlayer.
Constitution 12
The manufacturing method of a magnetic recording medium according to constitution 11, wherein said pre-coat layer is sputtered in a mixture gas atmosphere containing an inert gas and nitrogen.
Constitution 13
The manufacturing method of a magnetic recording medium according to constitution 12, wherein the content of nitrogen contained in the mixture gas is set at 20 to 80%.
Constitution 14
The manufacturing method of a magnetic recording medium according to any one of constitutions 11 to 13, wherein said substrate is a glass substrate.
According to the above constitution 1, the pre-coat layer is constituted by the lower layer containing Ni and P and the upper layer made of the Cr alloy. The layer of the lower layer containing Ni and P has a role for interrupting organic pollution substances on the substrate surface or alkali impurities immersed out from the substrate, and a role for canceling (interrupting a film formed thereon so as not to influence the crystal growth) a surface state (such as the crystal structure) of the substrate surface. To the layer of the lower layer containing Ni and P, another element can be added without departing from the above effect. For example, Al, B, Zr, Ti, or the like, can be mentioned. The contents of these elements are
Ayama Kenji
Horikawa Jun-ichi
Tomiyasu Hiroshi
Umezawa Teiichiro
Yokoyama Tomotaka
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Hoya Corporation
Rickman Holly
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