EFFECT OF INTERGRAIN EXCHANGE INTERACTION ON MAGNETIC-PROPERTIES IN ISOTROPIC ND-FE-B MAGNETS

The effect of intergrain exchange and magnetostatic interactions on remanence and coercivity is calculated numerically for an isotropic Nd-Fe-B model magnet composed of 8000 grains. The intergrain exchange interaction affects the magnetizing process markedly when the grain size L is small, but the magnetostatic interaction does not have substantial effects. The calculated remanence which takes the intergrain exchange interaction into account increases with decreasing L from M(s)/2 (M(s): the saturation magnetization) to M(s) and agrees roughly with the experimental results. The calculated coercivity decreases with decreasing L from 0.48 H(A) (H(A): the anisotropy field) to 0. Our results suggest that the large remanence above M(s)/2 observed experimentally in isotropic Nd-Fe-B magnets can be explained by the intergrain exchange interaction between Nd2Fe14B grains.