Toshihiro Mihara

Hot-pressed Mn-Zn ferrite for magnetic recording heads

Hot-pressed ferrites have been studied in connection with fabrication of a high quality head material. A two-step hot-pressing technique has enabled the preparation of hot-pressed ferrite with a porosity lower than 0.1 percent and an adjusted average grain size between 0.1 μm and 500 μm. The largest available ingot of hot-pressed ferrite is 120 mm in diameter and 20 mm in thickness. A hot-pressed Mn-Zn ferrite with an adjusted microstructure can be made with a μ m of 40 000 and an H c lower than 0.02 Oe. A hot-pressed Mn-Zn ferrite of another composition will have a B m greater than 5000 G and a μ 0 of 700 at 10 MHz. The effect of mechanical working on magnetic properties of hot-pressed ferrites, single-crystal ferrites, and high-density ferrites is also described. The lapping characteristics and the wear problems in a ferrite head of hot-pressed, single-crystal, and high-density ferrite are also discussed.

Sulfur Modified Chromium Dioxide

It was found that sulfur ions dissolved in chromium dioxide up to about 3 atomic percent lowering both the Curie temperature, Tc, and the saturation magnetization, σs. As the amount of sulfur increased, the lattice constant of the crystal, a0, increased from 4.423 A to about 4.435 A, while no change was observed for c0. The addition of sulfur did not change substantially the size of the powder. The coercive force, Hc, at room temperature was as much as 120 Oe. The combined addition of sulfur and tellurium, however, resulted in a fine acicular powder with a coercive force higher than 400 Oersted and a Curie temperature of about 100°C. This powder has potential use in thermal duplication of magnetic tape signals.

Temperature Variation of the Initial Permeability in Ni- and Ni-Zn-Ferrites Containing Excess Iron and Small Amounts of Cobalt

Some factors affecting the µ-T curve of Ni- or Ni-Zn-ferrites containing excess iron were studied. The µ-T curve of the ferrites is markedly affected not only by additions of Co, but also by the preparation procedure, apparently due to the oxidation of the ferrites. A possible cause of the effect of the oxidation is also discussed.

Sulfur modified chromium dioxide

Chromium dioxide modified with sulfur has been studied with the intention of obtaining a magnetic powder which is suitable for the tape of thermomagnetic duplication. Sulfur ions dissolve into CrO 2 up to about 0.17 wt.% and decrease the Curie temperature and saturation magnetization. With added sulfur of about 1 wt.%, the Tc of chromium dioxide is lowered by 20°C and the σ s becomes about 70 EMU/g. The lattice parameter a 0 increases with increasing sulfur, while c 0 shows no change. The CrO 2 with only a sulfur modifier does not have fine acicular shape. Therefore, the combined addition of S and Te was tried. The S-Te-modified CrO 2 has T c of 100°C, H c of 400 Oe and σ s of 81 EMU/g. The particle shape of this oxide is about 0.5 μm in average length and 10/1 in length to width ratio. This powder has high potential for use in the magnetic tape of thermal duplication.