Dowa Electronics Materials Co., Ltd.

Dowa Mining Co., Ltd.

Hiroshi Kimura

Kenji Masada

Takafumi Amino

Yuzo Ishikawa

A method for producing a magnetic powder comprised chiefly of FeNcomprising providing a starting powder comprising an oxy-hydroxide or oxide of iron and an amount of noble metal. The starting powder is reduced into an iron powder by a dry method using a hydrogen gas; and the iron powder is nitrided into a magnetic powder comprised chiefly of FeNparticles using a nitrogen-containing gas at a temperature not higher than 200&#xb0; C. The amount of noble metal is such that an amount that the atomic percent ratio of the noble metal content to Fe in the magnetic powder is 0.01-10.

Magnetic powder suitable for low-noise media

An iron nitride system magnetic powder comprising of particles comprised primarily of Fe16N(having an average particle diameter of up to 25 nm, for example) is provided, to which one or more elements selected from Si, P and Ti is adhered. The powder has a C/Fe atomic ratio of 0.5 to 30%, preferably a (Si+P+Ti)/Fe atomic ratio of 0.1 to 10%. With &#x394;Hc defined (Hc&#xb7;Hc)/Hc&#xd7;100, the powder has a &#x394;Hc of up to 5%, and with &#x394;&#x3c3;s defined as (&#x3c3;s&#xb7;&#x3c3;s)/&#x3c3;s&#xd7;100, a &#x394;&#x3c3;s of up to 20%. The powder can provide an ignition temperature of 140&#xb0; C. or above, and a tap density of 1.0 g/cmor above. Hcand &#x3c3;sare the coercive force (kA/m) and saturation magnetization (Am/kg), respectively, of the iron nitride system magnetic powder after adhesion, and Hcand &#x3c3;sare the coercive force (kA/m) and saturation magnetization (Am/kg), respectively, of the powder after it has been stored in a thermo-hygrostat for one week at a temperature of 60&#xb0; C. and a relative humidity of 90%.

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Okayama, Japan

Hiroshi Kimura