COERCIVITY OF GAMMA-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 Co 2+/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.