Experimental approach to coercivity analysis in hard magnetic materials

Abstract

Different processes may determine magnetization reversal in hard magnetic materials. The conditions under which these occur and their exact mechanisms are not well understood. In this paper some of the magnetic measurements which appear to be most meaningful are described and their implications with respect to physical processes involved are discussed. Whatever the exact coercivity mechanism is, the observed behavior is discussed using the concept of activation volume in which magnetization reversal is initiated. When the size of this volume is of the order of the size of the magnetic particles, it is suggested that collective magnetization processes are involved. The activation volume is on the contrary much smaller than magnetic particles and varies with temperature approximately as δ 3 when domain wall nucleation and propagation occur. The coercive field is deduced to be weak with respect to the anisotropy in the activation volume. The sign and the strength of dipolar interactions are discussed.