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.