Cation migration and coercivity in mixed copper-cobalt spinel ferrite powders

Mixed cobalt-copper spinel ferrites CoxCu1-xFe2O4 with acicular shape, prep ared from oxalate precursors at moderate temperatures, have been investigat ed by several techniques to relate the coercivity With structure. The catio n distribution in these ferrites is sensitive to the thermal history of the samples. Cation migration occurs during annealing in the 200-600 degrees C range in samples quenched from 710 degrees C and in the 350-600 degrees C range in slowly cooled samples. Because of shape anisotropy, tetragonal dis tortion, and directional order, coercivities from about 1500 to 4000 Oe are obtained in these ferrites. (C) 1998 Academic Press.