Temperature dependent magnetic properties of barium-ferrite thin-film recording media

Temperature dependencies of magnetic properties were measured in barium-ferrite thin films with grains having in-plane aligned as well as randomly oriented easy axes. The temperature dependence of H_c was shown to be similar to that of the effective anisotropy field, which is determined by the crystalline and shape anisotropies. The measured H _c values in the easy-axis aligned and randomly oriented films are significantly smaller than those predicted by the Stoner-Wohlfarth (SW) coherent rotation model. Such discrepancies are believed to be caused by incoherent rotation. Deviations from the SW model were also found within a wide temperature range in the angular dependence of coercivity and remanent coercivity, the field dependence of torque and rotational hysteresis. These led to the conclusion that temperature has only weak affects on the rotation mode of the magnetization. The discrepancies between the thermal activation volume and the grain size which were found previously at room temperature, and were believed to be yet another signature of incoherent rotation, were shown to also exist at a low temperature of 173 K