Fujifilm Corporation

Asahi Techno Glass Corporation

Fuji Photo Film Company, Limited

Akira Manabe

Masatoshi Takahashi

Hiroyuki Suzuki

Nobuo Yamazaki

Toshio Tada

Satoshi Matsubaguchi

Ayako Matsumoto

An aspect of the present invention relates to a hexagonal ferrite magnetic powder manufactured by a glass crystallization method as well as having an average plate diameter ranging from 15 to 25 nm, an average plate ratio ranging from 2.0 to 2.8 and a coercive force (Hc) ranging from 159 to 279 kA/m.

Hexagonal ferrite magnetic powder and method of manufacturing the same, and magnetic recording medium and method of manufacturing the same

A hexagonal ferrite magnetic powder having an average tabular diameter of from 15 to 28 nm, a coercive force (Hc) of from 2,000 to 5,000 Oe (from 160 to 400 kA/m), a switching field distribution (SFD) of from 0.3 to 0.7 and a D/Dof from 1.05 to 1.25. This magnetic powder can be obtained by melting and quenching starting materials to obtain an amorphous product, and thermally treating the product, which comprises increasing a temperature at a rate of 300 to 500&#xb0; C./hr in a temperature range of 550 to 600&#xb0; C. in the thermal treatment before the temperature reaches the thermally treating temperature.

Hexagonal ferrite magnetic powder, method for producing the same and magnetic recording medium

A hexagonal ferrite magnetic powder having an average tabular diameter of from 15 to 30 nm, a coercive force (Hc) of from 2,000 to 5,000 Oe (from 160 to 400 kA/m) and a saturated magnetization (&#x3c3;s) of equal to or more than the average tabular diameter (nm)&#xd7;0.37+45 A&#xb7;m/kg. This magnetic powder is obtained by melting a starting material containing a material which has a composition within the hatched region () in the triangular phase diagram shown in FIG.and quenching the molten product to obtain an amorphous product, subjecting the amorphous product to a thermal treatment, acid treatment, and washing. Also, a magnetic recording medium is obtained by adding this magnetic powder to the magnetic layer and coating it on the support.

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Shizuoka, Japan

Akira Manabe