Mitsuo Sugimoto

Amorphous characteristics in spinel ferrites containing glassy oxides

Abstract Various kinds of flake-shaped amorphous ferrites have been produced by adding glassy oxides to spinel ferrites and furthermore by a rapidly quenching the molten ferrite. Various kinds of amorphous ferrite thin films have also been produced on a glass plate by means of a vacuum evaporation method. It was found that the magnetization of amorphous spinel ferrites is very low at room temperature, but becomes significantly larger at liquid helium temperature. Amorphous ferrite thin film possesses a large perpendicular anisotropy and a relatively large polar Kerr rotation angle. The results are discussed in connection with the Mossbauer spectra and the magnetic structure.

Acicular barium ferrite particles useful for perpendicular magnetic recording

Abstract We have succeeded in the mass production of acicular Ba ferrite particles with a wide range of I H c values, from 500 to 4000 Oe, and with saturation magnetization values of 50 emu/g or more. These particles are very useful as perpendicular magnetic recording media because the direction of easy magnetization is perpendicular to the longitudinal direction of the particles. Acicular BaFe 12 O 19 was obtained through a topotactic reaction between FeOOH and BaCO 3 . The I H c value was adjusted by partial replacement of Fe 3+ with Co 2+ and Ti 4+ . With a composition of BaFe 10 CoTiO 19 , the I H c value was 500 Oe. In this paper, using magnetic torque curves, it is shown that a magnetically oriented sheet of acicular Ba ferrite particles has uniaxial anisotropy.

Perpendicular Magnetic Anisotropy of CoO x Films Prepared by Targets Facing Type of Sputtering

CoO<inf>x</inf> thin films with perpendicular magnetic anisotropy (PMA) were prepared at room temperature by the reactive facing-target sputtering technique. We investigated the PMA, coercivity and static magnetization process of the film samples, with the following results. (1) CoO<inf>x</inf> films with a columnar structure are composed of hep Co and fcc CoO. (2) The highest perpendicular anisotropy energy K<inf>u</inf> was 2.3×10⁶ erg/cm³. K<inf>u</inf> increases with increasing M<inf>s</inf>; the PMA of CoO<inf>x</inf> thin films is attributed to the magnetocrystalline anisotropy of Co. (3) Hca increases with decreasing diameter of columnar grains in CoO<inf>x</inf> thin films. (4) The dependence of H<inf>c¿</inf> on the direction of the applied magnetic field is similar to that expected from the Stoner-Wohlfarth model. The static magnetization process in CoO<inf>x</inf> thin films is mainly the rotational type.