Micro magnetic investigation of the relaxation process in hard magnetic materials

The relaxation of several micro magnetic model systems has been studied . Our results show that similarly to hysteresis, relaxation proceeds through the nucleation and propagation of domain wall-like structures involving a number of magnetic moments which is linked to the exchange correlation length of the material, the probability of magnetization reversal of simple homogeneous system is characterized by the occurrence of a 'waiting time'during which the macroscopic state of the system evolves very slowly and the time required to get probability one of magnetization reversal is, different from the predictions of the Arrhenius kinetics finite. Despite these departures from the predictions of the classic two-level description of the relaxation processes, the evolution at constant field and temperature of the magnetization of systems with distributed properties can be represented, in limited time intervals, by logarithmic laws similar to those commonly used when discussing experimental data. We analyze the relationships between the parameters describing these logarithmic laws and some characteristics of the magnetic moment configurations observed during relaxation. (author)