Magnetic powder, method for producing the same and magnetic recording medium comprising the same
AssigneeHitachi Maxell, Ltd.
InventorsMikio Kishimoto, Yuji Sasaki, Shinichi Kitahata, Yumiko Kitahata, Hideaki Watanabe
Life of this patent
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Abstract
A magnetic powder consisting of substantially spherical or ellipsoidal particles comprising a transition metal which comprises iron and a rear earth element which is mainly present in the outer layer of the magnetic powder particles, and having a particle size of 5 to 200 nm, a coercive force of 80 to 400 kA/m and a saturation magnetization of 10 to 25 μWb/g.
Claims31
A magnetic recording medium comprising a non-magnetic support, at least one undercoat layer containing an inorganic powder and a binder formed on said support, and a magnetic layer containing a magnetic powder and a binder formed on said at least one undercoat layer, wherein said magnetic layer has an average thickness of 0.3 μm or less, and said magnetic powder is a magnetic powder of substantially spherical or ellipsoidal particles comprising a transition metal which comprises iron and a rear earth element which is mainly present in the outer layer of the magnetic powder particles, and having a particle size of 5 to 200 nm, a coercive force of 80 to 400 kA/m and a saturation magnetization of 10 to 25 μWb/g.
A magnetic powder consisting of substantially spherical or ellipsoidal particles comprising a transition metal which comprises iron and a rear earth element which is mainly present in the outer layer of the magnetic powder particles, and having a particle size of 5 to 200 nm, a coercive force of 80 to 400 kA/m and a saturation magnetization of 10 to 25 μWb/g.
A method for producing a magnetic powder which contains a rare earth element and a transition metal comprising iron, said method comprising the steps of:
- dispersing substantially spherical or ellipsoidal particles of magnetite or cobalt ferrite in an aqueous solution containing at least a rare earth element ion to form a dispersion,
- adding an aqueous solution of an alkaline material to said dispersion in a molar amount sufficient for converting said rare earth element ion to a hydroxide to form a surface layer of the hydroxide on the particles of magnetite or cobalt ferrite,
- recovering the particles,
- drying and reducing the particles by heating to obtain substantially spherical or ellipsoidal particles having a particle size of 5 to 200 nm, a coercive force of 80 to 400 kA/m and a saturation magnetization of 10 to 25 μWb/g.
A method for producing a rare earth element-iron nitride magnetic powder comprising the steps of:
- supplying an iron hydroxide or an iron oxide in the form of particles as a raw material,
- depositing a rare earth element on the surface of the particles of the iron hydroxide or the iron oxide,
- reducing said particles carrying the rare earth element by heating, and
- nitriding said particles at a temperature lower than a temperature in the-reducing step.
Dependencies are inferred from the claim text.