Hoya Corporation

Tsuyoshi Watanabe

Masato Kobayashi

Teiichiro Umezawa

Hiroshi Tomiyasu

Masao Takano

Takashi Morikawa

Genshichi Hata

Koji Takahashi

Masashi Suzuki

Satoshi Yokota

There is disclosed a magnetic recording medium in which a seed layer, under layer, intermediate layer, first magnetic layer, nonmagnetic layer, second magnetic layer, protective layer, and lubricant layer are successively laminated on a glass substrate, the nonmagnetic layer is constituted of an alloy containing Cr and C, and the magnetic layer is constituted of an alloy containing Co and Pt. The under layer includes at least the seed layer for finely dividing the crystal particles of the magnetic layer, the seed layer includes at least two or more layers of nonmagnetic films, and the intermediate layer formed of the material different from that of the nonmagnetic film is interposed between the nonmagnetic films. In measurement of the thermal stability of the magnetic recording medium, a head is used, the head includes a read/write element, and a write track width is twice or more as large as a read track width in the head.

Magnetic recording medium, and thermal stability measuring method and apparatus of magnetic recording medium

In a magnetic recording medium, surface roughness of a glass substrate and the variation of the surface roughness are suppressed to the predetermined range. Namely, the surface roughness (Rmax, Ra, Rq) and the relation (Rmax/Ra) between Rmax and Ra are restricted to the predetermined range. In this event, Ra is representative of a center-line mean roughness, Rmax is defined as a maximum height representative of a difference between a highest point and a lowest point and Rq is representative of a root mean square roughness. Thereby, crystal grains of an underlying layer and a magnetic layer formed thereon are equalized. Specifically, the surface roughness is specified by Rmax&#x2266;15 nm, Ra&#x2266;1 nm and Rq&#x2266;1.5 nm. Further, the ratio between the surface roughness Rmax and the surface roughness Ra is specified by Rmax/Ra&#x2266;30.

Method of manufacturing a glass substrate and a magnetic recording medium

In a magnetic recording medium, surface roughness of a glass substrate and the variation of the surface roughness are suppressed. Namely, the surface roughness (Rmax, Ra, Rq) and the relation (Rmax/Ra) between Rmax and Ra are restricted. Ra is representative of a center-line mean roughness, Rmax is defined as a maximum height representative of a difference between a highest point and a lowest point and Rq is representative of a root mean square roughness. Thereby, crystal grains of an underlying layer and a magnetic layer formed thereon are equalized. The surface roughness is specified by Rmax&lE;15 nm, Ra&lE;1 nm and Rq&lE;1.5 nm and the ratio between the surface roughness Rmax and the surface roughness Ra is in the range of 10 to 30.

Glass substrate for information recording medium

Growing community of inventors

Singapore, Singapore

Tsuyoshi Watanabe