Microstructure and Coercivity of Nd-Fe-B Permanent Magnet

In order to clarify the mechanism underlying the coercivity in Nd-Fe-B magnets, the authors studied both the magnetic properties of a bcc phase which surrounds the main Nd2Fel4B phase in the material, and the appearance of reverse domains at crystal surfaces, grain boundaries and phase interfaces. The bcc phase, induced by annealing from the amorphous state, was found to have soft magnetic properties compared with the main phase. Formation of Nd and Tb layers on clean Nd-Fe-B surfaces resulted in greatly increased coercivity, indicating that the states of crystal surfaces and grain boundaries are indeed important in determining the coercive force.