Kenichi Nakata

US Patent:

6821618, Nov 23, 2004

Filed:

Jul 1, 2002

Appl. No.:

10/185728

Inventors:

Jun Koujima - Hiroshima-ken, JP
Teruaki Santoki - Ohtake, JP
Kenichi Nakata - Cupertino CA
Takanori Doi - Hatsukaichi, JP
Masaaki Maekawa - Hiroshima, JP
Kousaku Tamari - Cupertino CA

Assignee:

Toda Kogyo Corporation - Hiroshima-ken

International Classification:

C23C 1408

US Classification:

428332, 428336, 428694 T, 428694 TS, 2041921

Abstract:

A magnetic recording medium exhibiting a high coercive force and excellent squareness having a substrate, an underlayer formed on the substrate, and a spinel-type iron oxide thin film with maghemite as a main component formed on the underlayer. The spinel-type iron oxide thin film has a thickness (t) of 5 to 50 nm, is constituted by grains having an average grain size (D) of 5 to 30 nm, standard deviation of sizes of grain of not more than 4 nm and a ratio (D/t) of the average grain size (D) to the thickness (t) of less than 1. 0, exhibits a coercive force of not less than 159 kA/m (2,000 Oe) and a coercive squareness ratio S* of not less than 0. 5:1 in a longitudinal recording medium or a squareness ratio not less than 0. 75:1 in a perpendicular recording medium.