Nd-Fe-B磁石の磁化反転過程に及ぼす静磁気相互作用の影響 —計算機シミュレーション—

Magnetization reversal process of Nd-Fe-B sintered magnets was simulated based on the micromagnetic theory under consideration of the magnetostatic interaction and the cooperative effect of many grains. Reversal of magnetization was nucleated from magnetically soft grains. Then, the reversed region grew in the direction of applied field, and spread into the whole magnet when the applied field exceeded a critical value. The coercivity was decreased significantly by the existence of a small amount of magnetically soft grains, and did not depend on their fraction. Nonmagnetic inclusions between Nd2Fe14B grains also initiated magnetization reversal and decreased the coercivity. These effects of magnetostatic interaction were especially significant for the magnets with well-aligned grain orientation, and limited the obtainable coercivity to approximately 0.7 of the anisotropy field even if the magnet was consisted of perfect grains segregated from each other.