Magnetic Properties of Cobalt-Contained Iron Oxides (Part 3)

Acicular a-Fe2O3 and γ-Fe2O3 particles were treated at 70°C in alkali solution containing CO+2 and Fe2+ With CO2+/Fe2+ ratio of 0.5. The variation of particle shape and magnetic properties with progress of reaction was examined.In the use of a-Fe2O3 particles for starting material, the quantity of hydroxides decreased with the progress of reaction, and then cobalt-ferrite particles precipitated. The shape of cobalt-ferrite was cubic, and this cobalt-ferrite did not crystallize on a-Fe2O3 particles. The results of magnetic measurements of the particles precipitated in progress of reaction were explained by considering the growth of cobalt-ferrite particles from single-domain size to multi-domain size.In the use of γ-Fe2O3 particles for starting material, the quantity of hydroxides decreased with the progress of reaction, and the hydroxides finally disappeared. The resultant particles were acicular, and cubic particles were not observed. The results of magnetic measurements of the particles suggested that the, e cobalt-ferrite crystallized on the surface of γ-Fe2O3 particles. The origin of high coercivity of the resultant particles was discussed.