Specific Heat of Co₂TiO₄ and its Anomaly Associated with Magnetic Transition

Abstract

The specific heat of a ferrimagnet Co₂TiO₄ which has a spinel structure was measured between 2°K and room temperature. An anomalous heat due to a magnetic transition was observed. The Curie temperature is found to be 49.0°K. The total entropy of the transition is approximately Rln8 which suggests that the degeneracies of ground states of Co²⁺ ions in tetrahedral and octahedral sites are fourfold and twofold respectively. The Debye temperature is 560°K. The observed magnetic specific heat below about 30°K shows the modified T^3⁄2 dependence which is predicted from the spin wave theory taking into account the anisotropy energy, except at very low temperature. The effective anisotropy field, 2K⁄M_S, is 4.8×10⁴ Oe. The absolute magnitude of the exchange Interaction of the spin, 3/2, of a Co²⁺ ion in a tetrahedral site with the fictitious spin, 1/2, of a Co²⁺ ion in an octahedral site, J_AB′, is evaluated to be 3.23 k_B.