Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1998-10-07
2001-08-21
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S336000, C428S690000, C428S690000, C428S900000, C204S192200
Reexamination Certificate
active
06277484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to storage devices and, particularly, to magnetic recording media used in storage devices such as hard disks for computers, and a method for the production thereof.
2. Description of the Related Art
A magnetic recording medium used in a hard disk or the like is made up of a non-magnetic substrate and thin films of magnetic materials formed on the substrate. Performance of a thin magnetic layer is prone to be effected by the material of an underlying layer. It is thus common to provide an underlayer between a magnetic layer and a non-magnetic substrate in order to improve performance of the magnetic layer.
At present, a magnetic recording medium in which an underlayer of chromium (Cr), nickel (Ni), or an alloy based on them is formed on a non-magnetic substrate, and on which a film of alloy based on cobalt (Co), such as a Co—Cr—Ta alloy, Co—Cr—Pt alloy or the like, is formed, is used as a medium allowing a high storage density. Hard disks for computers are required to have large storage capacity, and to this end, it is required that magnetic recording media have a much higher storage density. Thus, magnetic recording media is required to have a higher coercivity and a reduced media noise.
On the other hand, magnetic recording media represented by hard disks are requested to have smoothness and resistance to shock due to a recent trend towards a small head flying height. Accordingly, glass substrates which are superior in those properties to the aluminum substrates predominantly used at present are attracted attention. Examples of magnetic recording media using a glass substrate are given in Japanese Unexamined Patent Publications No. 6-96431, No. 5-325163, etc., all of which use Cr or an alloy thereof for an underlayer under a magnetic layer. They also describe interposing an intermediate layer of Cu, Ti, Al or the like between the Cr layer and the glass substrate in order to improve the magnetic properties and the recording and read back properties. For example, Japanese Unexamined Patent Publication No. 6-96431 discloses a magnetic recording medium in which an intermediate layer of Cu or the like is interposed, so as to prevent oxygen and the like, from a substrate, from reaching a Cr underlayer and make (110) face of Cr parallel to the surface of a substrate, to thereby improve the magnetic and magnetic recording properties.
Japanese Unexamined Patent Publication (Kokai) No. 8-171716 discloses a magnetic recording medium in which an underlayer consisting of a compound of Ni and P is directly formed on a non-magnetic substrate. However, a magnetic recording medium in which a Ni-based non-magnetic compound is used for an underlayer, and an intermediate layer is interposed between a glass substrate and the underlayer, is not known.
SUMMARY OF THE INVENTION
In the aforementioned magnetic recording medium using the Cr alloy underlayer, as described in, for example, Japanese Unexamined Patent Publication No. 6-96431, it is required to heat the substrate during a manufacturing process to improve properties of the film of magnetic material, as described in its examples. Heating the substrate leads to the emission of adsorbed gases from the substrate and into the chamber for film formation, resulting in increased pressure in the chamber. Amounts and types of emitted gases vary depending on humidity and conditions of film deposition in the chamber, and these gases cause unstable properties of the formed magnetic film. Consequently, it is preferred that heating of the substrate is not carried out to obtain more stable properties.
In the aforementioned magnetic recording medium using the underlayer of an Ni-based compound (Japanese Unexamined Patent Publication (Kokai) No. 8-171716), the underlayer consisting of a compound of Ni and P is directly formed on the non-magnetic substrate. It has been found, by experiment, that the direct formation of an underlayer of Ni—P compound (Ni
3
P) results in poor adhesion between the underlayer and the substrate. (See Comparative Example 1 below.)
Thus, a magnetic recording medium which uses a glass substrate and has, in combination, superior magnetic and magnetic recording properties and good adhesion of an underlayer to the substrate, has not hitherto be attained.
Accordingly, the invention aims to provide a magnetic recording medium which has these desired properties in combination and is suitable for high storage density recording, to thereby meet a demand for much higher coercivity and reduced media noise to improve the storage density.
The invention provides a magnetic recording medium comprising a substrate, a magnetic layer of Co-based magnetic alloy, and an underlayer of Ni-based non-magnetic material interposed between the substrate and the magnetic layer, wherein the magnetic recording medium further comprises an intermediate layer of Cr between the substrate and the underlayer.
The magnetic recording medium of the invention is produced by a method which comprises providing a substrate, forming an intermediate layer of Cr on the substrate, forming an underlayer of Ni-based non-magnetic material on the intermediate layer, and forming a magnetic layer of Co-based magnetic alloy on the underlayer, wherein each of the layers is formed by a sputtering process at a sufficient pressure to promote granular growth of crystal of the layer.
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Chemical Segregation in CoNIPt(SiO2) Alloy Film; Akihiro Murayama and Masao Miyamura; Appl. Phys. Lett. vol. 65, No. 9; Aug. 29, 1994; pp. 1186-1188.
Magnetic Properties of Sputtered Co-Pt Thin Films; Masahiro Kitada and Noboru Shimizu; J. Appl. Phys. No. 12; Dec. 1983; pp. 7089-7094.
Mukai Ryoichi
Shimoda Kazumasa
Takeshita Hiroto
Fujitsu Limited
Greer Burns & Crain Ltd.
Kiliman Leszek
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