Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1999-03-25
2001-08-14
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S336000, C428S690000, C428S690000, C428S690000, C428S900000
Reexamination Certificate
active
06274233
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetic recording medium, and more specifically, the present invention relates to a magnetic recording medium having excellent noise properties.
BACKGROUND OF THE INVENTION
Most commercially available magnetic recording media are an in-plane magnetic recording media where the magnetic easy axis of the magnetic film is mainly oriented parallel to the substrate. If such an in-plane magnetic recording medium is fabricated to have a high recording density, the bit volume is excessively reduced and the reproduction properties may deteriorate due to a thermal fluctuation effect or the like. Furthermore, it is also known that media with high recording density suffer from an increase in the medium noise due to expansion of the magnetization reversal transition region or the like.
On the other hand, a so-called vertical magnetic recording medium where the magnetic easy axis in the magnetic film is oriented perpendicularly to the substrate is advantageous in that low noise can be attained even with high recording density. This is because a sharp magnetization transition is formed and as the recording density increases, the demagnetization field is decreased and stabilized. Moreover, high recording density can be attained even when the bit volume is relatively large. As such, the vertical magnetic recording medium is drawing the attention of investigators in this field.
However, the vertical magnetic recording medium has a reproduction waveform different from that of the in-plane magnetic recording medium. More specifically, the isolated waveform is not a single peak type but contains a di-pulse waveform. Accordingly, it is difficult to apply the signal processing system commonly used for in-plane recording media without modification.
To cope with this, a vertical and in-plane composite type magnetic recording medium has been proposed, which comprises both an in-plain magnetic film and a vertical magnetic film. Such structure enables the use of the same signal processing system as used for in-plane magnetic recording media.
In recent years, the demand for magnetic recording media with higher recording density has been increasing and in keeping with this tendency, there is a demand for improved noise properties.
However, conventional magnetic recording media are by no means entirely satisfactory with respect to noise properties, and there is also a demand for magnetic recording media having more excellent noise properties. The present invention has been achieved in consideration of the above problems of the prior art.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a magnetic recording medium adapted for use with the signal processing system commonly used for in-plane magnetic recording media without modification and having excellent noise properties.
The above object has been achieved in a first embodiment of the invention by providing a magnetic recording medium comprising a substrate having thereon an in-plane magnetic film having a magnetic easy axis oriented in the in-plane direction with respect to the substrate and a vertical magnetic film having a magnetic easy axis oriented perpendicularly to the substrate, the in-plane magnetic film being disposed closer to the substrate than the vertical magnetic film and having a coercivity Hc of from 1,500 to 4,000 Oe and a remnant magnetization film thickness product BrT of from 20 to 100 G&mgr;m, and the vertical magnetic film having a coercivity Hc of from 1,500 to 4,000 Oe and a thickness of from 100 to 1,000 Å.
In this first embodiment, the vertical magnetic film preferably has a thickness of from 100 to 600 Å and the in-plane magnetic film preferably has a remnant magnetization film thickness product BrT of from 20 to 50 G&mgr;m.
A separation film comprising a material capable of growing non-epitaxially to the in-plane magnetic film is preferably disposed between the in-plane magnetic film and the vertical magnetic film, and the separation film preferably has a thickness of from 5 to 200 Å.
A nonmagnetic intermediate layer having an hcp structure is preferably disposed between the separation film and the vertical magnetic film.
Furthermore, the clearance between the in-plane magnetic film and the vertical magnetic film is preferably from 10 to 500 Å.
In a second embodiment, the present invention provides a magnetic recording medium comprising a substrate having thereon an in-plane magnetic film having a magnetic easy axis oriented in the in-plane direction with respect to the substrate and a vertical magnetic film having a magnetic easy axis oriented perpendicularly to the substrate, the in-plane magnetic film being disposed closer to the substrate than the vertical magnetic film, a separation film being disposed between the in-plane magnetic film and the vertical magnetic film, and the separation film containing one or more of Ta, Re, CuTi, SiC, W, NiP, Zr, Ti and C as a main component.
In this second embodiment, the separation film preferably has a thickness of from 5 to 200 Å.
A nonmagnetic intermediate layer having an hcp structure is preferably disposed between the separation film and the vertical magnetic film.
Furthermore, an in-plane magnetic film underlayer is preferably disposed at the substrate side of the in-plane magnetic film, and the in-plane magnetic film underlayer preferably contains Cr or an alloy consisting of Cr and one or more of Ti, Mo, W and V, as a main component.
Furthermore, the in-plane magnetic film preferably contains a Co alloy consisting of from 12 to 25 at % of Cr, from 0 to 15 at % of Pt, from 1 to 10 at % of Ta, from 0 to 10 at % of one or more of Zr, Re, Cu and V, and the balance of Co, as a main component.
In a third embodiment, the present invention provides a magnetic recording medium a substrate having thereon an in-plane magnetic film having a magnetic easy axis oriented in the in-plane direction with respect to the substrate, a separation film comprising a material capable of growing non-epitaxially to the in-plane magnetic film, a nonmagnetic intermediate layer having an hcp structure and a vertical magnetic film having a magnetic easy axis oriented perpendicularly to the substrate, the nonmagnetic intermediate layer containing a Co alloy consisting of from 25 to 50 at % of Cr, from 0 to 15 at % of Pt, from 0 to 10 at % of one or more of Ta, Zr, Cu and Re, and the balance of Co, as a main component, and the vertical magnetic film containing a Co alloy consisting of from 16 to 30 at % of Cr, from 0 to 15 at % of Pt, from 2 to 10 at % of Ta, from 0 to 5 at % of Zr and the balance of Co, as a main component.
The nonmagnetic intermediate layer preferably has a thickness of from 20 to 400 Å.
Furthermore, the clearance between the in-plane magnetic film and the vertical magnetic film is preferably from 10 to 500 Å.
REFERENCES:
patent: 4801481 (1989-01-01), Sagoi
patent: 5665460 (1997-09-01), Sugita
patent: 5942309 (1999-08-01), Kamijo
patent: 5981039 (1999-11-01), Isono
patent: 63-090025 (1988-04-01), None
Osaka Tetsuya
Sakai Hiroshi
Sakawaki Akira
Yoshikawa Toshihiko
Kiliman Leszek
Showa Denko Kabushiki Kaisha
Sughrue Mion Zinn Macpeak & Seas, PLLC
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