Effect of Intergrain Exchange Interaction on Magnetic Properties in Isotropic Nd-Fe-B Magnets

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Abstract
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.