Coercivity enhancements by high-magnetic-field annealing in sintered Nd-Fe-B magnets

An influence of a high-field annealing on the magnetic properties was investigated in sintered Nd-Fe-B magnets. When the sample B, containing 0.32 at. % Al, was annealed at T-a=550degreesC under a magnetic field of H-a=140 kOe and then cooled without field, the coercivity H-c increased by 25% with respect to the control sample annealed at zero field. As for the sample C, containing both Cu 0.13 at. % and Al 0.32 at. %, higher H-c values were obtained when it was annealed at T-a=550degreesC and the field of H-a=140 kOe was kept applied down to the room temperature. These results were discussed in terms of a field-induced change in interface matching between Nd2Fe14B and intergranular phases. (C) 2004 American Institute of Physics.