Temperature dependence of post-sintered annealing on magnetic properties of intergranular phase in Nd-Fe-B permanent magnet

Abstract

Post-sinter-annealing temperature (Ta) dependences of the chemical and magnetic properties of intergranular (grain boundary; GB) phase in a Nd14.0Fe79.7B6.2Cu0.1 sintered magnet have been investigated by x-ray absorption spectroscopy and its magnetic circular dichroism. A relative change of the Cu concentration in the GB phase is found to depend on Ta and shows the maximum at Ta = 500 °C. The Ta-dependence of the Cu concentration was very similar to that of the coercivity. On the other hand, there is no significant Ta-dependence for the magnetization at the fracture surface: the Fe magnetic moment is 1.7 ± 0.036 μB at all Ta. The Cu-rich layer segregated in the GB phase would have a key role in the coercivity enhancement of the Nd-Fe-B sintered magnet.