Hysteresis and thermal relaxation in random anisotropy systems

Recent experimental studies shown that relaxation and hysteresis phenomena at elevated temperatures measured on soft nanocrystalline materials (Finemet-type) with low crystalline fraction, cannot be described by a single activation volume. To clarify the nature of the magnetization processes in these materials we studied the behavior of clusters of grains with random anisotropy in which a direct correspondence between zero-temperature switching fields h c , energy barriers ΔF and activation moments Δm, is involved, namely: ΔF ∼ Δm 1/2 : h c ∼ Δm 1/2 . We show that some aspects of the dynamics of field-rate-dependent hysteresis loops observed in real systems can be reproduced by choosing simple distributions of cluster size.