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 0.48H_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.