Temperature Dependence of Coercivity at Recording Frequencies: Barium Ferrite versus Oxide

We demonstrate that materials with comparable thermal dependence of coercivity under normal laboratory measurement conditions, differing only in sign, have quite different properties at recording frequencies. Barium ferrites, with positive dH_c/dT, have augmented thermal dependence, while oxides, with negative dH_c/dT, exhibit weaker thermal dependence at recording frequencies. Experimental data and theoretical analysis confirm this behavior. Two methods of predicting coercivity as a function of temperature, for recording time scales, are presented. The implications for direct overwrite performance while thermally cycling are discussed.