Field dependence of the thermal remagnetization in sintered hard magnets

Abstract

The dependence of the thermal remagnetization (TR) in sintered hard magnets on external magnetic fields has been investigated in order to determine more precisely the grain-interaction fields in the DC-demagnetized state. That negative external field at which the TR or its initial slope vanishes or changes its sign, corresponds well to the theoretical parameter σ f, i.e. the distribution width of internal field fluctuations. For the “normal” TR of the metallic magnets SmCo 5, Sm 2Co 17 and NdFeB these fields are of the order of −0.5, 0.25 and −0.04 T , respectively. For the “inverse” TR at the hard ferrites this external field is about −0.02 T . The systematic variation of the TR-curves with a small external field is well explained by our theoretical model and leads to a refinement of the parameters for SmCo 5 and barium ferrite. Susceptibility measurements with small alternating fields, carried out at different points of the TR curve, as well as repeating TR-experiments at SmCo 5 demonstrate clearly that the TR is mainly due to the contribution of the “weak” grains, remagnetizing in the interaction fields of the “hard” grains.