Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-05-14
2001-09-11
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192160
Reexamination Certificate
active
06287429
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a magnetic recording medium for use in recording information at a high density. It is to be noted throughout the instant specification that a magnetic disk will be mainly described as an example of the magnetic recording medium hereinunder and will be included in a magnetic disk device, although this invention is not restricted to the magnetic disk or the magnetic disk device.
A magnetic disk of the type described, comprises a non-magnetic substrate and a magnetic layer. A cobalt-platinum (Co—Pt) alloy is generally used as the magnetic layer. In order to record information at a high recording density on the magnetic disk, it is necessary to increase a characteristic of magnetism such as a coercive force (Hc) and a product of remanence and a thickness of the magnetic layer. A conventional magnetic disk of the above-mentioned type is disclosed in Journal of the Institute of Television Engineer of Japan, Vol. 40, No. 6, 1986, pages 475 to 480, and will be referred to as a first conventional magnetic disk.
The first conventional magnetic disk comprises the non-magnetic substrate of a glass and the magnetic layer of Co—Pt—Mo. The magnetic layer is directly formed on the non-magnetic substrate. It is possible to control the coercive force within a wide range by the changing of the amount of Mo and to record information at a high recording density in the first conventional magnetic disk.
When the amount of Mo increases in the magnetic layer of the first conventional magnetic disk, a reduction has been observed in the coercive force of the first conventional magnetic disk. For example, the coercive force of the first conventional magnetic disk becomes to about 350 oersteds when Mo is included in the magnetic layer at about 14 atomic percents. In addition, a saturation magnetic flux density reduces in the first conventional magnetic disk in proportion as Mo increases in the magnetic layer. As a result, the product of remanence and thickness of the magnetic layer reduces.
As described above, it is difficult to increase the coercive force and the product of remanence and thickness of the magnetic layer in the first conventional magnetic disk. Namely, it is difficult to record information at a high recording density.
Another conventional magnetic disk is disclosed in Japanese Patent Publication No. Heisei 4-16848, namely, 16848/1992 and will be referred to as a second conventional magnetic disk. The second conventional magnetic disk comprises the non-magnetic substrate, an intermediate layer formed on the non-magnetic substrate, and the magnetic layer formed on the intermediate layer. The intermediate layer consists of a Cr—V alloy or a Cr—Fe alloy. The magnetic layer consists of the Co—Pt alloy. It is possible to increase the coercive force and to make a rectangular magnetization curve be improved in the second conventional magnetic disk.
However, the coercive force is about 1600 oersteds at a maximum level in the second conventional magnetic disk. The maximum level is not enough as the coercive force on recording information at the high recording density.
Still another conventional magnetic disk is disclosed in Journal of the Applied Physics, 67(12), 15 June 1990, pages 7507 to 7509 and will be referred to as a third conventional magnetic disk. The third conventional magnetic disk comprises the non-magnetic substrate, the intermediate layer of a Cr—Mo alloy, and the magnetic layer of a Co—Ni—Cr alloy.
However, the coercive force is about 1120 oersteds in the third conventional magnetic disk. As a result, it is difficult to record information at the high recording density.
As readily understood from the above description, it is difficult to record information at high recording density in each of the first through the third magnetic disk. Namely, it is difficult to render characteristic of magnetism great in each of the first through the third magnetic disk.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a magnetic medium capable of improving a magnetic characteristic.
Other objects of this invention will become clear as the description proceeds.
According to a first aspect of this invention, there is provided a magnetic recording medium comprising a non-magnetic substrate having a principal surface, an intermediate layer formed on the principal surface, and a magnetic layer formed on the intermediate layer. The intermediate layer comprises an intermediate material composed of chromium and molybdenum. The magnetic layer comprises a magnetic material composed of cobalt and platinum.
In the first aspect of this invention, Cr and Mo become a solid solution in the intermediate layer. Lattices in the intermediate layer expand according to the amount of Mo so that a lattice distance on (110) face of Cr approaches the (002) face of the magnetic layer comprising Co and Pt. As a result, it is possible to improve coercive force in the magnetic layer inasmuch as orientation in the magnetic layer is changed.
The magnetic material may be further composed of Mo. When the magnetic material is composed of Co, Pt, and Mo, the coercive force increases on the basis of a pinning effect of a magnetic wall and by promoting a magnetic isolation of magnetic particles. Furthermore, the coercive force also increases by micronizing the magnetic particles. When the coercive force increases, a peak width becomes small in reproduction. As a result, a media noise decreases. In addition, a width of a zigzag wall decreases by increasing a pinning number when the magnetic material is further composed of Mo. As a result, the media noise also decreases.
When both of the intermediate and the magnetic layers include Mo, Mo is easily diffused on a boundary face of the intermediate layer and the magnetic layer. As a result, the magnetic isolation of magnetic particles is further promoted. In addition, it is possible to increase bond strength between the intermediate layer and the magnetic layer.
The magnetic material may be further composed of at least one element selected from the group consisting of tantalum, boron, chromium, oxygen, nitrogen, niobium, manganese, zinc, wolfram, plumbum, rhenium, vanadium, and zirconium.
The intermediate material may be further composed of at least one element selected from the group consisting of wolfram, boron, vanadium, niobium, tantalum, iron, nickel, rhenium, copper, zirconium, zinc, phosphorus, silicon, gallium, germanium, hafnium, aluminum, and titanium. When the intermediate layer includes an additional element or additional elements in addition to Cr and Mo, the additional element is not easily solved to Cr or Mo in the intermediate layer. As a result, promotion occurs in micronization of crystal particles and isolation of crystal particles inasmuch as the additional element segregates on a grain boundaries of the crystal particles in the intermediate layer. Accordingly, promotion occurs in micronization and magnetic isolation of crystal particles so that the coercive force increases and the media noise decreases.
According to a second aspect of this invention, there is provided a magnetic recording medium comprising a non-magnetic substrate having a principal surface, a first intermediate layer formed on the principal surface, a second intermediate layer formed on the first intermediate layer, and a magnetic layer formed on the second intermediate layer. The first intermediate layer comprises a first intermediate material composed of chromium. The second intermediate layer comprises a second intermediate material composed of chromium and molybdenum. The magnetic layer comprises a magnetic material composed of cobalt and platinum.
In the second aspect of this invention, it is possible to homogenize the number of crystal particles in the second intermediate layer and to homogenize the number of crystal particles in the magnetic intermediate layer. As a result, it is possible to decrease the media noise and to improve the magnetic characteristic.
REFERENCES:
patent: 4438066 (1984-03-01), Aboaf et al.
patent:
Horikawa Jun-ichi
Kobayashi Masato
Moroishi Keiji
Nozawa Osamu
Hoya Corporation
Ladas and Parry
Nguyen Nam
VerSteeg Steven H.
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