Toda Kogyo Corporation

Kousaku Tamari

Takanori Doi

Kenichi Nakata

Yasuo Kakihara

Setsuo Yamamoto

Mitsuru Matsuura

Kenji Okinaka

Yasutaka Ota

Norimichi Nagai

Jun Koujima

Kohji Mori

Teruaki Santoki

Akio Mishima

Hirofumi Kawasaki

Mamoru Tanihara

Kunio Ikemoto

Tsutomu Katamoto

Masaaki Maekawa

A magnetic recording medium exhibiting a high coercive force and excellent squareness having a substrate, an underlayer formed on the substrate, and a spinel-type iron oxide thin film with maghemite as a main component formed on the underlayer. The spinel-type iron oxide thin film has a thickness (t) of 5 to 50 nm, is constituted by grains having an average grain size (D) of 5 to 30 nm, standard deviation of sizes of grain of not more than 4 nm and a ratio (D/t) of the average grain size (D) to the thickness (t) of less than 1.0, exhibits a coercive force of not less than 159 kA/m (2,000 Oe) and a coercive squareness ratio S* of not less than 0.5:1 in a longitudinal recording medium or a squareness ratio not less than 0.75:1 in a perpendicular recording medium.

Magnetic recording medium and process for producing the same

A magnetic recording medium including a substrate and formed on the substrate a maghemite thin film having a surface roughness represented by a center line mean roughness Ra of 0.1 to 1.0 nm, and a coercive force squareness S* value of not less than 0.50. This magnetic recording medium exhibits excellent magnetic properties, especially, coercive force squareness S* value and a more enhanced surface smoothness.

A magnetic recording medium is prepared by forming on a plastic substrate, a nickel oxide underlayer having a plane (200) which is predominantly oriented in parallel with the surface of the plastic substrate, then forming on the nickel oxide underlayer at a substrate temperature of less 240&deg; C., a cobalt-containing magnetite thin film having a plane (400) which is predominantly oriented in parallel with the surface of the plastic substrate, and finally oxidizing the cobalt-containing magnetite thin film in a plasma-activated oxygen atmosphere containing a rare gas at a substrate temperature of less than 240&deg; C. while incorporating the rare gas into oxygen. This results in a cobalt-containing maghemite thin film as a perpendicular magnetic film having a spacing of a plane (400) of not more than 2.082 &angst;. The magnetic recording medium so produced is useful for high-density recording using a plastic substrate.

Process for producing magnetic recording medium

A magnetic recording medium of the present invention comprises: a plastic substrate; and a cobalt-containing maghemite thin film formed on said substrate, containing cobalt at a molar ratio of cobalt to iron of not more than 0.06:1, and having either a spacing of a plane (,) of not more than 2.510 &angst;, a spacing of a plane (,) of not more than 2.415 &angst; or a spacing of a plane (,) of not more than 2.950 &angst;; and has a coercive force of not less than 2,000 Oe. Such magnetic recording medium suitably applicable to existent magnetic recording systems using a ring-type magnetic head and capable of using a plastic substrate for providing a magnetic recording medium for high-density recording.

A magnetic recording medium of the present invention comprises: a substrate; and a cobalt-containing maghemite thin film formed on said substrate, containing cobalt at a molar ratio of cobalt to iron of not more than 0.06:1, having either a spacing of a (311) plane of not more than 2.510 .ANG., a spacing of a (222) plane of not more than 2.415 .ANG. or a spacing of a (220) plane of not more than 2.950 .ANG., and having a coercive force of not less than 1,800 Oe. Such a magnetic recording medium has as high a coercive force as possible, specifically not less than 1,800 Oe, and exhibits an excellent stability independent to change in passage of time and a large output in a high recording frequency region.

Magnetic recording medium

A magnetic recording medium of the present invention comprises: a substrate; a nickel oxide underlayer formed on said substrate; and a cobalt-containing maghemite thin film formed on said nickel oxide underlayer, having either a spacing of a (311) plane of not more than 2.510 .ANG., a spacing of a (222) plane of not more than 2.415 .ANG. or a spacing of a (220) plane of not more than 2.950 .ANG., and having the ratio of either of X-ray diffraction spectrum peak intensities of the (311), (222) or (220) planes of said cobalt-containing maghemite thin film to an X-ray diffraction spectrum peak intensity of the (400) plane of more than 0.5:1. Such a magnetic recording medium has a higher coercive force, a higher saturation magnetization, less amount of noise generated, a large output in a high recording frequency region and less distortion of a reproduced waveform, and is suitable for use in current magnetic recording systems in which a ring-type magnetic write head is used.

The disclosure describes a magnetic recording medium comprising: a substrate; an NiO primary layer which is formed on the substrate and in which the plane (200) is substantially oriented in parallel with the surface of the substrate; and a Co-containing maghemite thin film which is formed on the NiO primary layer and in which the plane (400) is substantially oriented in parallel with the surface of the substrate, the molar ratio of Co to Fe is not less than 0.01 to less than 0.10, and the spacing of the plane (400) is not more than 2.082 .ANG..

Disclosed herein is a perpendicular magnetic film comprising a spinel thin film which is formed on a substrate, which contains Fe as the main ingredient and further contains Co and Ni, and which has a coercive force of less than 3000 Oe, the plane (400) thereof being predominantly oriented in parallel with said substrate, the spacing of the plane (400) being not more than 2.082 .ANG., the molar ratio of Co to Fe being 0.005 to 0.32 and the molar ratio of Ni to Co being at least 0.6.

Process for producing perpendicular magnetic film

The disclosure describes a magnetic recording medium comprising:

Disclosed herein is a perpendicular magnetic film comprising at least two of a (A)/(B) unit or (B)/(A) unit obtained by disposing a spinel type crystal layer (A) represented by the following general formula:

Perpendicular magnetic film, process for producing the same and magnetic

Disclosed herein is a perpendicular magnetic film comprising a Co-containing .gamma.-Fe.sub.2 O.sub.3 film formed on a substrate in which the plane (400) is predominantly oriented in parallel with said substrate, the molar ratio of Co to Fe is between 0.01 and 0.32, the spacing of said plane (400) is not more than 2.084 .ANG., and the optical absorption coefficient at 700 nm is not more than 2.5 .mu.m.sup.-1.

Perpendicular magnetic film and multi-layered film for perpendicular

Perpendicular magnetic film, multilayered film for perpendicular

Disclosed herein are acicular magnetic iron based alloy particles for magnetic recording, containing 1.5 to 10 mol % of B based on Fe (calculated as B) and 1.5 to 10 mol % of Co based on Fe (calculated as Co) in the vicinity of the surfaces of said particles and having a saturation magnetization of not less than 125 emu/g and an S.F.D. value of not more than 0.50, and a process for producing the same.

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Hiroshima, Japan

Kousaku Tamari