Magnetic recording medium

Details Magnetic recording medium Magnetic recording medium

1999-01-08

2001-07-03

Pianalto, Bernard (Department: 1762)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S617000, C428S621000, C428S661000, C428S662000, C428S663000, C428S664000, C428S665000, C428S666000, C428S667000, C428S678000, C428S690000, C428S690000, C428S697000, C428S699000, C428S900000, C428S928000

Reexamination Certificate

active

06255006

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a magnetic recording medium such as a magnetic drum, a magnetic tape and a magnetic disc. More specifically, the present invention relates to a magnetic recording medium having excellent noise properties and high coercivity.
BACKGROUND OF THE INVENTION
In recent years, magnetic disc devices or the like have tended toward higher densities, and accompanying this, a magnetic head based on a high magnetic resistance effect (hereinafter referred to as a “MR head”) has been used in many cases. To accommodate such magnetic disc devices, the magnetic recording medium must also exhibit excellent magnetic properties such as low noise.
This is because the MR head has high read sensitivity and low head noise as compared with conventional magnetoelectric induction type heads. For improving the properties of the magnetic disc device and the like, such as S/N ratio and recording density, the magnetic recording medium must also have excellent magnetic properties such as low noise properties.
The magnetic recording medium commonly used at present comprises a substrate comprising an Al alloy having formed thereon an NiP plating film, a non-magnetic undercoat film comprising Cr or the like formed on the substrate, a magnetic film comprising a material containing Co as a main component formed on the undercoat film, and a protective film and a lubricant film formed thereon.
This kind of magnetic recording medium is disclosed in JP-B-5-24564 (the term “JP-B” as used herein means an “examined Japanese patent publication”). The magnetic recording medium disclosed in this patent publication exhibits improved squareness by providing a non-magnetic undercoat film comprising Cr and having a thickness of from 50 to 200 Å.
Furthermore, JP-A-1-232522 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) proposes a magnetic recording medium including a non-magnetic undercoat film comprising an alloy obtained by adding one or more metals selected from Cu, Nb, Ti, V, Zr, Mo, Zn, W and Ta to Cr and having a thickness of from 500 to 3,000 Å, to thereby improve magnetic properties, particularly coercivity.
However, in the magnetic recording medium disclosed in JP-B-5-24564, the thickness of the non-magnetic undercoat film comprising Cr is small and accordingly, the crystals growing in this undercoat film are not sufficiently oriented toward the (
200
) direction. As a result, orientation of the crystals within the magnetic film, which epitaxially grow on the undercoat film, is disordered and the magnetic recording medium thus obtained disadvantageously fails to provide satisfactory magnetic properties such as coercivity.
In the magnetic recording medium disclosed in JP-A-1-232522, the thickness of the non-magnetic undercoat film comprising a Cr alloy is large and at the time of forming the film, bulking of crystals comprising a Cr alloy takes place within the film. In turn, magnetic grains within the magnetic film formed on the non-magnetic undercoat film are bulked due to epitaxial growth on the non-magnetic undercoat film comprising the bulked Cr alloy crystals. As a result, the magnetic recording medium thus obtained disadvantageously has deteriorated magnetic properties such as deteriorated noise properties.
The present invention has been achieved in view of the above problems of the prior art.
SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide a magnetic recording medium having both high coercivity and excellent noise properties.
The above object of the present invention is attained by providing a magnetic recording medium comprising a non-magnetic substrate having thereon a non-magnetic undercoat and a magnetic film, said magnetic film comprising a material containing Co as a main component, said non-magnetic undercoat comprising at least two layers including a first undercoat film and a second undercoat film provided on said first undercoat film, said first undercoat film comprising a material containing Cr as a main component, and said second undercoat film comprising a material selected from the group consisting of a Cr/Nb-base alloy, a Cr/W-base alloy, a Cr/V-base alloy and a Cr/Mo-base alloy as a main component.
When the second undercoat film comprises a material containing a Cr/Nb-base alloy as a main component, the Nb content of the second undercoat film is preferably from 5 to 20 at %.
When the second undercoat film comprises a material containing a Cr/W-base alloy as a main component, the W content of the second undercoat film is preferably from 5 to 60 at %, more preferably from 3 to 60 at %.
When the second undercoat film comprises a material containing a Cr/V-base alloy as a main component, the V content of the second undercoat film is preferably from 2 to 30 at %.
When the second undercoat film comprises a material containing a Cr/Mo-base alloy as a main component, the Mo content of the second undercoat film is preferably from 2 to 25 at %.
The first undercoat film preferably has a thickness of from 25 to 600 Å, and the second undercoat film preferably has a thickness of from 1 to 200 Å.
The non-magnetic substrate preferably comprises glass or an aluminum alloy h having a NiP plating layer applied to the surf ace thereof.


REFERENCES:
patent: 4833020 (1989-05-01), Shiroishi et al.
patent: 5356522 (1994-10-01), Lal et al.
patent: 582 412 (1994-02-01), None
patent: 751 501 (1997-01-01), None

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