Kabushiki Kaisha Toshiba

Tokyo Shibaura Denki Kabushiki Kaisha

Hirotaka Yokoyama

Tadashi Ido

Takeo Ito

Toshihiko Oguchi

Osamu Kubo

Tatsumi Maeda

Tutomu Nomura

Shunji Kurisu

Moriyasu Wada

Akio Ishizawa

Hirohisa Kato

Yoshiyasu Koike

A magnetic recording medium having a nonmagnetic supporting member and a plurality of magnetic layers formed on at least one major surface of the nonmagnetic supporting member, comprising a first longitudinally oriented magnetic layer having a first longitudinally orientation rate located uppermost and comprising a hexagonal system ferromagnetic powder, and a second longitudinally oriented magnetic layer having a second longitudinally orientation rate located between the nonmagnetic supporting member and the first longitudinally oriented magnetic layer and comprising a needle-like crystal magnetic powder, wherein the first longitudinally orientation rate of the first longitudinally oriented magnetic layer is at least 0.5 and is smaller than the second longitudinally orientation rate of the second longitudinally oriented magnetic layer.

Magnetic recording medium and a method for producing the same wherein

Disclosed is a magnetic powder for high-density magnetic recording, formed of a substituted hexagonal ferrite possessing an average particle diameter in the range of 0.01 to 0.2 .mu.m and a coercivity in the range of 200 to 2,000 Oe and characterized by the fact that the substituted hexagonal ferrite has at least 0.05 to 0.5 atom of at least one element selected from the group consisting of Zr and Hf per chemical formula and at least one element selected from among the elements other than Zr and Hf substituted for part of the Fe atom of the ferrite, and a magnetic recording medium of the present invention comprises a substrate and the magnetic powder mentioned above deposited on the substrate. Since the magnetic powder comprises very minute particles, the magnetic powder and the magnetic recording medium are capable of high-density recording. The magnetic powder has an improved desirably controlled aspect ratio for orientation and the temperature characteristic of coercivity (Hc) as compared with the countertype formed of a hexagonal ferrite which has neither Zr nor Hf substituted for the Fe atom.

Magnetic recording medium containing a substituted hexagonal ferrite

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.

A magnetic powder for magnetic recording media comprises a hexagonal crystalline system ferrite containing, as essential components for said hexagonal crystalline system ferrite, iron and oxygen, and at least one of the elements selected from the group of Ba, Sr, Ca and Pb, said iron being substituted by at least one of the elements selected from the group of Ti, Co, Ni, Mn, Cu, Zn, In, Ge, Nb, Zr and Sb; and at least one of Ba, Sr, Ca, Pb being substituted by at least one of the rare earth elements selected from the group of Ce, Pr, Nd, Pm, Sm and Eu. The magnetic powder has a mean particle size of 0.01 to 0.3 .mu.m and a coercive force of 200 and 2000 Oe. The magnetic powder is improved in its saturation magnetization while retaining a suitable coercive force. Accordingly, high reproduction output can be obtained in a magnetic recording medium employing the magnetic powder.

Magnetic powders for magnetic recording media and magnetic recording

To manufacture a perpendicular magnetic recording medium, a nonmagnetic substrate having a coating layer of a binder with magnetic particles dispersed therein is passed through a magnetic field in a direction substantially perpendicular thereto, and a perpendicular orientation of the magnetic particles is performed as the substrate passes through an upstream region of the magnetic field. A viscosity of the coating layer is increased in a downstream region of the magnetic field, thereby restricting further movement of the magnetic particles in the coating layer before the nonmagnetic substrate is removed from the magnetic field.

Method and apparatus for perpendicular magnetic recording medium

Disclosed is a magnetic recording medium comprising substrate and a resinous composition containing magnetic particles of uniaxially-anisotropic hexagonal crystals having particle diameters of 0.01.about.0.3 .mu.m and coated on said substrate; the ratio of remanent magnetization to saturation magnetization on the magnetization curve corrected to demagnetizing field which is measured in a direction vertical to the surface of the recording medium, ranging from 0.3 to 0.7. This magnetic recording medium requires no orientation treatment for its production.

Growing community of inventors

Yokosuka, Japan

Hirotaka Yokoyama