Nd-Fe-B系焼結磁石の強磁場熱処理と保磁力

抄録

  Results of a systematic study concerned with the high-magnetic-field effects on the coercivity in processing various series of sintered Nd-Fe-B magnets are given. Coercivity enhancement phenomenon was observed in several series of sintered Nd-Fe-B magnets with Cu additive after annealing under magnetic fields of 10~14 T. A strong correlation was suggested between the field annealing temperature at which maximum coercivity increase was observed and the anomaly temperature in differential scanning calorimetry experiments. We found a linear relation between the room temperature coercivity H_c of the sample annealed at T_a=500℃ under magnetic field H_a for a series of samples with different Dy contents, which can be expressed as H_c=H_c(0)+ α H_a, with H_c(0) being the value for the zero-field-annealed sample and α, the coercivity enhancement factor. Although very small, α has a positive finite value in samples with 0 mass% and 2 mass% Dy. Significant increase in α value was confirmed for samples with Dy content larger than 6 mass%. This suggests the effects of higher anisotropy in paramagnetic susceptibility of Nd-rich intergranular phase containing Dy. Also introduced is the preliminary results of the grain boundary diffusion process of sinterd Nd-Fe-B samples with surface Dy layer under strong gradient magnetic fields produced by the 18 T superconducting magnets.