THERMAL-BEHAVIOR AND MAGNETIC-PROPERTIES OF ACICULAR COPPER-COBALT FERRITE PARTICLES

CoxCu1-xFe2O4 (0 less than or equal to x < 0.3) ferrite particles were prepared by a soft chemistry method using oxalic precursors. The ferr ite particles obtained by this process are acicular in shape (4.2 less than or equal to L/D less than or equal to 4.6) ranging in length bet ween 1.5 and 0.8 mu m for 0 less than or equal to x less than or equal to 0.3. Two series of samples were investigated: a first sample (SC) grouped together the ferrites slowly cooled from 710 degrees C, and th e second (Q) consisted of samples quenched from the same temperature. In contrast to the stability of the SC ferrites, the Q ferrites are su bjected to two phenomena before reaching 400 degrees C. The first is a scribed to the migration of Cu2+ ions from tetrahedral to octahedral s ites. The second is the oxidation of Cu+ ions formed above 600 degrees C during the preparation process and frozen by quenching at room temp erature in the Q samples, Above approximately 400 degrees C, no differ ences appear to subsist between SC and Q samples. They are both subjec ted to diffusionless order-disorder transformation, due to the modifie d orientation of the Jahn-Teller distorsions, and to the migration of Cu2+ ions from octahedral to tetrahedral sites, before the Curie tempe rature is reached. Magnetic measurements performed on the samples prep ared for the present work reveal remarkably high and stable coerciviti es. These magnetic properties are due not only to the structural aniso tropy, but also to the morphological characteristics. Because of their high and stable coercivities, submicron copper ferrites could be inte resting pigments for magnetic recording. (C) 1995 Academic Press, Inc.