Cation Migration and Coercivity in Mixed Copper–Cobalt Spinel Ferrite Powders

Mixed cobalt–copper spinel ferrites Co x Cu1−x Fe2O4with acicular shape, prepared from oxalate precursors at moderate temperatures, have been investigated by several techniques to relate the coercivity with structure. The cation distribution in these ferrites is sensitive to the thermal history of the samples. Cation migration occurs during annealing in the 200–600°C range in samples quenched from 710°C and in the 350–600°C range in slowly cooled samples. Because of shape anisotropy, tetragonal distortion, and directional order, coercivities from about 1500 to 4000 Oe are obtained in these ferrites.