The preparation of Nd2Fe14B permanent magnetic powder with a fine microstructure has been tried by mechanical grinding (MG) and subsequent heat treatment. The decomposition of Nd2Fe14B phase into α-Fe and an amorphous phase was observed after MG. The powder annealed in vacuum after MG was composed of much finer grains than single magnetic domain size of about 300nm, and its coercivity was as high as 0.76MA/m. On the other hand, the coercivity of the powder annealed in Ar after MG was as low as 0.2MA/m, though it was also composed of much finer grains than single magnetic domain size. And the remarkable increment of oxygen content in the specimen was observed by the heat treatment in Ar. Such a remarkable increment of oxygen content resulted in the existence of large amounts of α-Fe and neodymium oxide. These phases caused the low coercivity. It was also found that MG time influenced the hard magnetic properties. In this work, the best MG time was confirmed to be 72ks.
