Effects of orientation and interaction of grains on coercivity for sintered NdFeB magnets

The coercivity of NdFeB magnets is determined by the coercivity of individu al grains and the interaction between the grains composed of the magnets. T he coercivity of individual grains and the intergrain interaction depend on the degree of the grain alignment. "tan theta type" Gaussian function is a pplied to describing the degree of the grain alignment. According to differ ent coercivity mechanisms, there are different formula on the coercivity an d the angular dependence of coercivity. The interaction between grains can be classified as the long-range magnetostatic interaction and the exchange- coupling interaction of neighboring grains. For the sintered magnet, the gr ain size is large and the grain boundaries are mostly separated by the non- magnetic phase. So, the long-range magnetostatic interaction is much strong er than the exchange coupling interaction and it makes the coercivity of th e magnet composed of misaligned grains be bigger than that of the magnet co mposed of ideally aligned grains. The effects of coercivity of individual g rains and the intergrain interactions are taken into account, and the start ing field theory is in agreement with the experimental result for the coerc ivity of sintered NdFeB magnets.