Toshinobu Sueyoshi

Coercivity of γ‐Fe2O3 particles growing iron‐cobalt ferrite

Acicular γ‐Fe2O3 particles were heated at 90°C in alkali solution containing Co2+ and Fe2+. The coercivity of the resultant particles remarkably increased with the increasing Co2+/Fe2+ ratio, and in the neighborhood of the Co2+/Fe2+ ratio of 0.4, reached a maximum value. When the particles with a Co2+/Fe2+ ratio of 0.5 were dissolved in hydrochloric acid, the cobalt content and the coercivity were rapidly decreased with increasing dissolved weight. Iron‐cobalt ferrite was expected to grow on the surface of γ‐Fe2O3 particles. The increase of coercivity was attributed to the iron‐cobalt ferrite.

Preparation and magnetic properties of Fe-Co fine particles

Fe-Co fine particles with high Co content were prepared by reducing Co-substituted iron oxide particles. The saturation magnetization of the particles increased with Co concentration. The saturation magnetization was 153.8 emu/g with 15.0 wt.% Co content compared to 133.0 emu/g for iron particles with the same surface area. The Fe-Co particles showed superior corrosion resistance compared to iron particles. A Co-ferrite layer formed on the surface of the particles helped minimize the progress of the oxidation. >

Effect of heat-treatment on magnetic properties and morphology of iron particles (2)

Abstract Marked inhibition effect of surface coated silica on the crystal of hematite particles in the process of heat-treatment of goethite particles was reduced by the addition of calcium hydroxide to the silica-coat on the surface of goethite particles. Coercivity of iron particles, prepared by reduction of the hematite particles, significantly decreased with increase in crystallite size of iron particles.

Magnetic Properties of Cobalt-Contained Iron Oxides (Part 1)

Acicular γ-Fe2O3 particles were treated at 90°C in alkali solution containing CO2+ and Fe2+. The coercivity of resultant particles remarkably increased with increasing CO2+/Fe2+ ratio, and reached a maximum value in the vicinity of 0.4 to 0.5. The increase of coercivity was attributed to the magnetic anisotropy of iron-cobalt ferrite which was considered to crystallize at the surface of γ-Fe2O3. The magnetic properties of γ-Fe2O3 particles coated by iron-cobalt ferrite, such as a variation of coercivity in annealing at 60°C or printing effect, were extremely stable compared with those of cobalt-substituted iron oxides.