Magnetization process : model of the potential function in the case of a thermal demagnetization

2014 The model of the potential function V(x), for the hysteresis cycles in a weak field of a ferromagnetic sample, demagnetized by an alternating field, leads to Rayleigh’s laws. In the case of a thermal demagnetization, the Bloch wall may be present in every well of V(x), and the domain structure is initially metastable. Considering all configurations where we can find the Bloch wall, in Néel’s formulation, we study the effect of a magnetic field on such a domain structure. We show that Rayleigh’s laws should no longer hold and that, for instance, the first remanence should vary with the amplitude of the cycle as the sum of a linear and a quadratic term. The structure is stabilized when the first cycle is over, but the limit cycle is shifted to the side where the field is applied initially. We compare these results with Preisach’s grains model, extended to the case of thermal demagnetization. J. Physique 44 (1983) 871-878 JUILLET 1983,