Hazime Machida

Cobalt‐titanium substituted barium ferrite films for magneto‐optical memory

We have studied Faraday rotation and magnetic properties of Co‐Ti substituted barium ferrite films with perpendicular anisotropy, which were prepared by targets‐facing‐type sputtering method on (111) oriented GGG substrates. Faraday rotation (θF) of 500–830 nm was measured by using the Faraday modulation method. It was found that θF increased proportionally to the content of cobalt in the wavelength range 700–830 nm. In the BaFe10.42Co0.78Ti0.8O19 film, Faraday rotation and magnetic properties were as follows: θF=0.75 deg/μm at 780 nm, anisotropy field: Hk=5.2 kOe, coercive force: Hc=800 Oe, Curie temperature: TC=380 °C. Thermomagnetic recording was achieved on this film by using a 780‐nm laser diode. As a result, 2.0‐μm bit patterns were observed by Faraday effect.

Magneto-optical properties and thermomagnetic recording of M-type Ba-ferrites

Abstract Thermomagnetic recording by Ar laser was achieved on a Ba-ferrite perpendicular film. The Faraday rotation of a Co-Ti substituted Ba-ferrite single crystal was 0.83° / μm at λ = 0.78 μm .

Magnetic recording and playback apparatus of perpendicular recording type

A magnetic recording and playback apparatus of perpendicular recording type comprises a main pole having a magnetic axis which is normal to a recording surface of a magnetic record medium, an auxiliary magnetic pole disposed in surrounding relationship with the main pole with a small clearance from the lateral side thereof, a coil disposed on part of the auxiliary pole, and a yoke having its one end connected to the auxiliary pole and having its other end of a relatively large area disposed in opposite relationship with the recording surface of the record medium. The free end of the main pole is disposed in contact with the surface of the record medium while the yoke is disposed at a given distance from the surface of the record medium. During a recording operation, a current is passed through the coil in accordance with information to be recorded. Thereupon, a magnetic flux is concentrated in the free end of the main pole to cause an inversion of magnetization in that region of a magnetic layer of the record medium which is contacted by the main pole, thus recording the information. During a playback operation, the free end of the main pole picks up a magnetic flux which depends on the magnetization, representing the information, recorded in the magnetic layer of the record medium, producing a corresponding current flow through the coil. An output current from the coil is utilized for reproduction of the recorded information.

Magneto-Optical and Magnetic Properties of Co-Substituted BaM

BaM(BaFe12O19) has strong crystal anisotropy, but its Faraday rotation is low at only 0.22 deg/¿m (¿= 780 nm). An attempt to improve the properties of this material as magneto-optical recording media by replacing part of the Fe in BaM with Co is discussed. It was found that ¿F increased with the amount of Co substituted. The investigation confirmed that Co is effective in increasing BaM ¿F. When La is used for Co charge compensation, along with increasing ¿F, it was also found that the crystal anisotropy becomes high, and the properties of the material as magneto-optical recording media improved.