Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2002-08-15
2004-04-20
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S900000, C427S128000, C427S131000
Reexamination Certificate
active
06723458
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium, a method of manufacture therefor, and a magnetic read/write apparatus using the magnetic recording medium.
2. Description of the Related Art
Most magnetic recording media now commercially available are in-plane magnetic recording media wherein the axis of easy magnetization in a magnetic film is generally oriented parallel to the substrate.
In an in-plane magnetic recording medium, there is a possibility that the volume of recording bits will be too small when the recording density is increased and magnetic read/write characteristics are deteriorated by the thermal fluctuation effect. Also medium noise increases under the influence of diamagnetism at the boundary of recording bits when the recording density is increased.
In a so-called perpendicular magnetic recording medium of which the axis of easy magnetization in the magnetic film is generally oriented perpendicular to the substrate, in contrast, recording magnetic domains that have clear boundaries can be formed due to less influence of demagnetizing field at the boundary of recording bits even when the recording density is increased, and therefore noise can be reduced. Moreover, since the recording density can be increased even if the volume of bits is relatively large, the perpendicular magnetic recording medium has high thermal stability, resulting in much attention being given to the perpendicular magnetic recording medium. Consequently, structure of a medium suitable for use in perpendicular magnetic recording has been proposed.
Recently, there has been increasing demand for high-density recording in magnetic recording media. For this reason, a magnetic recording medium has been proposed in which a layer made of a soft magnetic material, called a soft back layer, is provided between a perpendicular magnetic film that serves as a recording layer and a substrate so as to improve the efficiency of the flow of the magnetic flux between a single pole type head and the magnetic recording medium, in order to use the single pole type head which has high capability of writing in the perpendicular magnetic film.
However, even when the soft back layer is provided, the magnetic recording medium does not have satisfactory performance in read/write characteristics, thermal stability, and the resolution, and therefore a magnetic recording medium that is improved in these characteristics has been desired.
Japanese Patent Application, First Publication, No. Sho 59-61012 proposes to add Cu as a third element to a perpendicular magnetic film made of a CoCr material. However, this magnetic recording medium has small perpendicular magnetic anisotropy constant Ku and was insufficient in read/write characteristics and thermal stability.
BRIEF SUMMARY OF THE INVENTION
Under the above-described circumstances, the present invention has been made, and an object thereof is to provide a magnetic recording medium that is capable of recording and reading back information at a higher density by improving the read/write characteristics and thermal stability, a method of manufacture therefor, and a magnetic read/write apparatus.
To achieve the object described above, the present invention employed the following constructions.
The magnetic recording medium of the present invention comprises at least an orientation control film that controls the orientation of a film provided directly thereabove, a perpendicular magnetic film, of which the axis of easy magnetization is generally oriented perpendicular to a non-magnetic substrate, and a protective film, that are provided on the non-magnetic substrate, wherein the perpendicular magnetic film is made of a material which contains Co, Cr, Pt and Cu, the Cr content being 16 at % to 24 at % and the Cu content being 0.1 at % to 4 at %, and a coercive force (Hc) of the perpendicular magnetic film being at least 3000 (Oe), negative nucleation field (−Hn) being 0 (Oe) to 2500 (Oe), and a ratio of residual magnetization (Mr) to saturation magnetization (Ms) being at least 0.85.
The perpendicular magnetic film preferably has a Cr content from 18 at % to 24 at %, a Pt content from 14 at % to 24 at %, and a Cu content from 0.1 at % to 3 at %.
The perpendicular magnetic film may comprise at least one of CoCrPtCu alloy, CoCrPtCuTa alloy, CoCrPtCuB alloy and CoCrPtCuTaB alloy.
In the present invention, a hard magnetic film made of a hard magnetic material can be provided between the non-magnetic substrate and the soft magnetic undercoat film.
In the present invention, a magnetizing stabilization film made of a soft magnetic material can be provided above the perpendicular magnetic film.
The method of manufacturing a magnetic recording medium of the present invention comprises forming at least an orientation control film that controls the orientation of a film provided directly thereabove, a perpendicular magnetic film of which axis of easy magnetization is generally oriented perpendicular to a non-magnetic substrate, and a protective film, on the non-magnetic substrate, while controlling so that the perpendicular magnetic film is made of a material which contains Co, Cr, Pt and Cu, the Cr content is 16 at % to 24 at % and the Cu content is 0.1 at % to 4 at %, and that a coercive force (Hc) of the perpendicular magnetic film is at least 3000 (Oe), negative nucleation field (−Hn) is 0 (Oe) to 2500 (Oe), and a ratio of residual magnetization (Mr) to saturation magnetization (Ms) is at least 0.85.
The magnetic read/write apparatus of the present invention comprises a magnetic recording medium and a magnetic head that records information on the magnetic recording medium and reads back the information, wherein the magnetic head is a single pole type head and the magnetic recording medium comprises at least an orientation control film that controls the orientation of a film provided directly thereabove, a perpendicular magnetic film, of which the axis of easy magnetization is generally oriented perpendicular to a non-magnetic substrate, and a protective film, that are provided on the non-magnetic substrate, wherein
the perpendicular magnetic film is made of a material which contains Co, Cr, Pt and Cu, the Cr content being 16 at % to 24 at % and the Cu content being 0.1 at % to 4 at %, and
a coercive force (Hc) of the perpendicular magnetic film being at least 3000 (Oe), negative nucleation field (−Hn) being 0 (Oe) to 2500 (Oe), and a ratio of residual magnetization (Mr) to saturation magnetization (Ms) is at least 0.85.
As described above, in the magnetic recording medium of the present invention, the perpendicular magnetic film is made of a material which contains Co, Cr, Pt and Cu, the Cr content being 16 at % to 24 at % and the Cu content being 0.1 to 4 at %. Therefore, read/write characteristics can be improved, and moreover, and thermal stability can be improved.
REFERENCES:
patent: 2002/0037441 (2002-03-01), Okuyama et al.
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Patent Abstracts of Japan, abstracting JP-A-6-180834, Ju
Hikosaka Takashi
Mochizuki Hiro
Nakamura Futoshi
Sakai Hiroshi
Sakawaki Akira
Rickman Holly
Showa Denko K.K.
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