Stock material or miscellaneous articles – All metal or with adjacent metals – Having magnetic properties – or preformed fiber orientation...
Reexamination Certificate
1997-05-06
2002-01-01
Mayes, Curtis (Department: 1734)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having magnetic properties, or preformed fiber orientation...
C428S668000, C428S928000, C360S135000
Reexamination Certificate
active
06335103
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to magnetic recording media such as magnetic recording tapes, floppy disks, magnetic recording disks, etc., a process for producing the same, and magnetic memory apparatuses using the magnetic recording media, and more particularly to magnetic recording media for longitudinal recording suitable for high density magnetic recording, a process for producing the same and magnetic memory apparatuses.
Heretofore, magnetic recording media using a metallic magnetic film have been proposed as magnetic recording-media for longitudinal recording for high density magnetic recording, as disclosed in Japanese Patent Publication No. 54-33523. Processes for forming magnetic recording media for longitudinal recording include an evaporation process, a sputtering process, a plating process, an ion beam sputtering process, etc.
Recently, needs for higher density recording and higher reliability have been increased. For example, magnetic recording media for longitudinal recording with a thin metallic magnetic film having an inplane coercivity as high as about 700 Oe and a high corrosion resistance at a high temperature and a high humidity, such as thin metallic magnetic film of magnetic alloy, e.g. Co-Pt, Co-Cr-Pt, Co-Ta-Pt, Co-Si-Pt, Co-Zr-Pt, Co-Hf-Pt, etc. have been proposed as in Japanese Patent Applications Kokai (Laid-open) Nos. 60-111323, 59-177725, 59-8806, etc.
Furthermore, it has been proposed to improve static magnetic properties such as an inplane coercivity Hc, a squareness S, a coercive squareness S*, etc. For example, it has been proposed to form a pure metal layer of Cr, Mo, W, Nh, W, etc. or an alloy layer of Cr-V, Cr-Fe, etc. as an underlayer on a substrate and form a magnetic recording layer of Co-Pt alloy or Co-Cr-Pt alloy thereon, an disclosed in Japanese Patent Application Kokai (Laid- open) No. 62-257617 (=U.S. Pat. No. 4,654,276), or to form a magnetic recording layer of Co-Cr-Pt alloy on a Ni-P underlayer, as disclosed in Japanese Patent Application Kokai (Laid-open) No. 59-88806, or to form an alumite underlayer on a substrate of aluminum alloy and form a magnetic recording layer of cobalt (Co)-based alloy comprising 3 to 15 at.% of at least Mo, V and W, 3 to 20 at.% of Cr and 3 to 15 at.% of a noble metal element such as Pt. Rh, Ru, Re, Pd, Ir, etc., the balance being at least 75 at.% of Co, thereon, as disclosed in Japanese Patent Applications Kokai (Laid-open) Nos. 61-246917 and 61-253622.
Furthermore, Japanese Patent Application Kokai (Laid-open) No. 62-257617 (=U.S. Pat. No. 4,654,276) and Japanese Patent Application Kokai (Laid-open) No. 62-257618 (=U.S. Pat. No. 4,652,499) disclose that when a magnetic recording layer of Co-Pt or Co-Cr-Pt is produced on a non-magnetic underlayer having a thickness of about 50 nm, such as Cr-V underlayer or W underlayer, the inplane coercivity Hc can be made higher than 1,200 Oe and also the coercive squareness S* higher than 0.9.
SUMMARY OF THE INVENTION
The main object of the present invention is to improve the corrosion resistance of a metallic magnetic layer and also to increase the inplane coercivity and the coercive squareness, thereby obtaining a higher density magnetic recording and a higher read output. Magnetic recording media of the prior art generally have such a disadvantage that the media noise tends to increase with a higher density magnetic recording and a higher read output. Particularly with a recent higher density magnetic recording, the recording frequency has been increased and the band width has been broadened, and consequently the head noise and amplifier noise tend to increase. Thus, it has been desired to develop magnetic recording media having smaller noise characteristics than these noises, while maintaining a higher read output.
As the result of extensive studies, the present inventors have found that an increase in the inplane coercivity and coercive squareness can increase the read and write characteristics at a higher density, but also can increase the noise and thus is not always advantageous with respect to the signal-to-noise ratio, and that particularly the noise considerably increases when the coercive squareness is made more than 0.9. Thus, in order to obtain magnetic recording media for longitudinal recording with distinguished read and write characteristics, it is essential to satisfy these mutually contradicting magnetic properties at the same time, and it is a current task to satisfy an inplane coercivity Hc of not less than 1,200 Oe and a coercive squareness S* of not more than 0.9, preferably not more than 0.85 at the same time. A coercive squareness S* means a ratio of H to Hc (H/Hc) at a cross point of a tangent line drawn at the point of inplane coercivity Hc in a magnetic hysteresis loop with a straight line drawn at the point of remanence magnetization Mr and in parallel to the magnetic field (H) axis.
A first object of the present invention is to provide magnetic recording media for longitudinal recording with less noises, a distinguished S/N ratio and a high reliability in corrosion resistance, etc.
A second object of the present invention is to provide magnetic recording media for longitudinal recording with a high inplane coercivity Hc, that is, at least 1,200 Oe and a small coercive squareness S*, that is, not more than 0.9, preferably not more than 0.85, which can read and write in a high S/N ratio even at a high density recording and has a high reliability, that is, high corrosion resistance and antiwear properties.
A third object of the present invention is to provide a process for producing magnetic recording media for longitudinal recording that can attain the second object of the present invention.
A fourth object of the present invention is to provide magnetic memory apparatuses using the magnetic recording media for longitudinal recording that can attain the first or second object or both objects of the present invention.
The first object of the present invention can be attained by making a magnetic layer mainly from an alloy comprising Co, a material X composed of at least one element selected from the first group consisting of Cr, Mo and W, a material Y′ composed of at least one element selected from the second group consisting of Ti, Zr, Hf, Ta, Nb, Ru and Rh, and a material Z composed of at least one element selected from the third group consisting of Al and Si. The alloy of the magnetic layer is represented by the following general formula:
(Co
1-a
X
a
)
1-b-c
Y′
b
Z
c
,
wherein it is desirable that a concentration of X on the basis of Co, that is, 100a, is 3 at.% to 20 at.% and concentrations of Y′ and Z on the basis of the sum total of Co and X, that is, 100b and 10c, are 1 at.% to 15 at.% and 1 at.% to 15 at.%, respectively, where the concentration of inevitable impurities is disregarded. Furthermore, it is desirable that the magnetic layer contains 0.1 at.% to 15 at.% of oxygen.
Furthermore, it is particularly desirable with respect to an improvement of inplane coercivity to provide an intermediate layer of nonmagnetic material composed mainly of at least one of Cr, Mo and W, and their alloys such as Cr-Ti, etc. between the magnetic layer and the nonmagnetic substrate. With magnetic recording media of the foregoing structure, magnetic memory apparatuses of high capacity with a high reliability can be provided.
The effects of the magnetic layer of the foregoing structure can be obtained through the following functions. The functions of the present invention will be explained below, referring to use of a body centered cubic (bcc) metal such as alloys composed mainly of at least one of Cr, Mo and W and their alloys such as Cr-Ti, etc. as an underlayer. On the underlayer, the axis of magnetic anisotropy of Co is oriented to have an inplane anisotropic component so as to give a high inplane coercivity. Furthermore, by addition of at least 3 at.% of Cr, etc. to Co in the magnetic layer, a high inplane coercivity, for example, about 500 Oe or higher, can be obtained. With increasi
Hishiyama Sadao
Matsuda Yoshibumi
Ohno Tomoyuki
Ohura Masaki
Shige Noriyuki
Beall Law Offices
Gray Linda L
Mayes Curtis
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