Kabushiki Kaisha Toshiba

Shunji Kurisu

Tatsumi Maeda

Etsuji Ogawa

Osamu Kubo

Tadashi Ido

Tutomu Nomura

Hirotaka Yokoyama

A magnetic powder is disclosed which is characterized by possessing a powder compression characteristic such that the magnetic powder, after being packed in a closed container, pressed at a load of 400 kgf/cm.sup.3, and relieved of the load, exhibits a packing density in the range of 2.5 to 3.5 g/cm.sup.3 and a geometric standard deviation of not more than 1.5 in the particle diameter distribution. A magnetic recording medium using the magnetic powder mentioned above has high packing and, consequently, secures high output, and has ample diminution of noise.

Hexagonal system ferrite powder for a high density magnetic recording

An object of the present invention is to provide a magnetic powder for magnetic recording and a magnetic recording medium wherein stability of a coercive force of each of the magnetic powder and the magnetic recording medium is improved. The magnetic powder for magnetic recording and the magnetic recording medium having the magnetic powder used therfor are characterized in that the magnetic powder is composed mainly of a plate-shaped ferrite having a crystalline anisotropy and containing an element effective for reducing a temperature coefficient of coercive force of the magnetic powder, and that a difference between a coercive force (Hc) of the magnetic powder at a room temperature and a coercive force (Hc(s)) of the magnetic powder in such a state that the magnetic powder is dispersively deposited on the surface of silica (SiO.sub.2) powder particles is 100 (Oe) or less.

Method of providing hexagonal ferrite magnetic powder with enhanced

A magnetic powder is disclosed which is characterized by possessing a powder compression characteristic such that the magnetic powder, after being packed in a closed container, pressed at a load of 400 kgf/cm.sup.3 and relieved of the load, exhibits a packing density in the range of 2.5 to 3.5 g/cm.sup.3 and a geometric standard deviation of not more than 1.5 in the particle diameter distribution. A magnetic recording medium using the magnetic powder mentioned above has high packing and, consequently, secures high output, and has ample diminution of noise.

High density magnetic recording medium containing hexagonal system

A magnetic powder for magnetic recording is disclosed which comprises composite magnetic particles (A), each of which contains hexagonal ferrite and spinel structure ferrite, and single phase magnetic particles of hexagonal ferrite (B). When the mixing ratio [(A):(B)] of (A) and (B) in the range from 5:95 to 95:5, remarkable effect can be obtained. Especially, when the mixing ratio of (A) and (B) is in the range from 5:95 to 30:70, the dispersion property is improved due to disturbance of magnetic stacking. Thus, the magnetic powder in this mixing ratio is particularly suitable for magnetic recording in a short wavelength range. When the mixing ratio of (A) and (B) is in the range from 70:30 to 95:5, the reproduction output is improved due to activation of (A). Thus, the magnetic powder in this mixing ratio is specifically suitable for magnetic recording in a long wavelength range. By containing the magnetic powder described above, a perpendicular magnetic recording medium with high electromagnetic characteristics, particularly a high S/N ratio and a low noise can be obtained.

Magnetic powder for magnetic recording and magnetic recording medium

A magnetic powder for magnetic recording is disclosed which comprises composite type magnetic particles (A), each of which contains hexagonal ferrite and spinel structure ferrite, and single phase type magnetic particles of hexagonal ferrite (B). When the mixing ratio of (A) and (B) in the range from 5:95 to 95:5, remarkable effect can be obtained. Especially, when the mixing ratio of (A) and (B) is in the range from 5:95 to 30:70, the dispersion property is improved due to disturbance of magnetic stacking. Thus, the magnetic powder in this mixing ratio is particularly suitable for magnetic recording in a short wavelength range. When the mixing ratio of (A) and (B) is in the range 70: 30 to 95:5, the reproduction output is improved due to activation of (A) . Thus, the magnetic powder in this mixing ratio is specifically suitable for magnetic recording in a long wavelength range. By containing the magnetic powder described above, a perpendicular magnetic recording medium with high electromagnetic characteristics, particularly a high S/N ratio and a low noise can be obtained.

A magnetic recording powder comprising a hexagonal barium ferrite substituted with a coercive force control element. This magnetic powder is preliminarily treated with sulfate ion-containing water so as to convert any free barium ions in the magnetic powder to a water insoluble compound such as BaSO.sub.4 or BaS.sub.2 O.sub.7. There is also proposed a magnetic recording medium having a magnetic layer containing such a magnetic powder as mentioned above.

Magnetic recording powder, method of manufacturing thereof and

A matnetic recording powder comprising a hexagonal barium ferrite substituted with a coercive force control element. This magnetic powder is preliminarily treated with sulfate ion-containing water so as to convert any free barium ions in the magnetic powder to a water insoluble compound such as BaSO.sub.4 or BaS.sub.2 O.sub.7. There is also proposed a magnetic recording medium having a magnetic layer containing such a magnetic powder as mentioned above.

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Yokohama, Japan

Shunji Kurisu