Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1998-05-11
2001-01-16
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S336000, C428S690000, C428S690000, C428S900000, C420S441000, C420S445000, C420S450000, C204S192200, C204S298120
Reexamination Certificate
active
06174598
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, and more particularly, to a magnetic recording medium having reduced medium noise.
BACKGROUND OF THE INVENTION
In recent years, the density of magnetic disc devices or the like has increased. To accommodate such higher densities, there is a need for a magnetic recording medium (hereinafter sometimes referred to as a “medium”) suitable for a magnetic head (hereinafter referred to as a “MR head”) using a high magnetic resistance effect that is capable of high reproduction sensitivity.
The MR head has low head noise as compared with conventional magnetoelectric induction type heads. Therefore, the reduction of medium noise has become very important for improving the S/N of the device as a whole.
In a magnetic recording disc for a hard disc device (HDD) commonly used at present, a non-magnetic underlayer (e.g., Cr, Cr alloy), a magnetic layer (e.g., CoCrTa, CoCrPtTa alloy) and a protective layer (e.g., carbon) are provided in sequence on a non-magnetic substrate. Also, a lubricating layer comprising a liquid lubricant is formed thereon.
In order to optimize the recording/reproducing properties of the above-described magnetic recording medium, JP-B-5-23564 (the term “JP-B” as used herein means an “examined Japanese patent publication”) proposes a Cr underlayer having a thickness of from 50 to 200 Å in order to increase squareness.
Furthermore, JP-A-1-232522 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) proposes to add one or more metals selected from Cu, Nb, Ti, V, Zr, Mo, Zn, W and Ta to the Cr underlayer in order to enhance the magnetic properties, and particularly coercive force.
Furthermore, EP 0,704,839A1 proposes to use an alloy having a B2 ordered structure (e.g., AlNi, AlCo, AlFe) as the underlayer to reduce the crystal size of the magnetic layer and thereby provide improved noise characteristics.
When the Cr underlayer is formed having a thickness of from 50 to 200 Å as proposed in JP-B-5-23564, the Cr crystal structure is not fully oriented toward the (200) plane. As a result, sufficiently high coercivity cannot be obtained and the medium is not suitable for a MR head.
In JP-A-1-232522, the thickness of the Cr underlayer is from 500 to 3,000 Å so that the Cr grains can be oriented toward the (200) plane. Consequently, the noise can be reduced. Furthermore, although Cr or a Cr alloy is used as the non-magnetic underlayer of the smoothened substrate, problems arise in that the anisotropy controlling effect of the disc by texturing or the like is lowered to cause a reduction in coercivity and in turn a decrease in the reproduction output.
When an Al alloy having a B2 ordered structure (e.g., AlNi, AlCo, AlFe, etc.) is used as an underlayer, as proposed in EP 0,704,839A1, the crystal size of the magnetic layer is reduced due to the Al—Ni alloy or Al—Co alloy and the noise is improved. However, it is difficult to increase coercivity using the Al—Ni alloy or to increase coercive squareness using Al—Co alloy. Accordingly, the reproduction output is small. Thus, a problem still remains in performing high density recording.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a magnetic recording medium suitable for a MR head, having both reduced noise and high coercivity.
The present inventors studied the characteristics of the Al—Ni alloy by adding thereto various elements and as a result, discovered that by adding a predetermined amount of Cr, Mo, W, V, Zr, Nb or Pd, a low noise magnetic recording medium having high coercivity (Hc) can be obtained. The present invention has been achieved based on these findings.
That is, the present invention solves the above problems of the prior art by providing a magnetic recording medium comprising a non-magnetic substrate having thereon a first non-magnetic underlayer and a magnetic layer comprising a Co alloy provided on the non-magnetic underlayer, wherein said non-magnetic underlayer comprises an alloy represented by the formula: (Ni
50
Al)
100−X
M
X
(wherein M is one or more of Cr (X=1-40 at %), Mo (X=1-50 at %), W (X=1-60 at %), V (X=1-35 at %), Zr (X=1-25 at %), Nb (X=1-35 at %) and Pd (X=1-25 at %), and when M comprises two or more of Cr, Mo, W, V, Zr, Nb and Pd, X is from 1 to 60 at %. As used herein, “at %” means “atom %”.
In a preferred embodiment, the magnetic recording medium further comprises a protective layer provided on the magnetic layer. Also, when M comprises two or more of Cr, Mo, W, V, Zr, Nb and Pd, X is preferably from 1 t 50 at %.
REFERENCES:
patent: 5302434 (1994-04-01), Doerner
patent: 5900324 (1999-05-01), Moroishi
patent: 5939202 (1999-08-01), Atoke
Kanazawa Hiroshi
Onami Kazunori
Sakai Hiroshi
Suzuki Mikio
Kiliman Leszek
Showa Denko Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
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