Low-Temperature Annealing Patterns and Demagnetization Curves in Sintered Nd-Fe-B Magnets

Abstract

  In order to trace the annealing temperature dependence of the coercivity in sintered Nd-Fe-B magnets systemtically, we examined a single successive annealing (SSA) method, in which the coercivity value of a single sample is successively recorded after each annealing cycle at T_a= 400°C-710°C with increments of ΔT_a = 10°C. In addition to the coercivity values, we paid special attention to the shapes of demagnetization curves, in terms of the differential susceptibility versus magnetic field plot, which provides information on the nucleation field distribution (NFD). Samples with small amounts of Cu additives showed a more significant temperature dependence of the coercivity than those without Cu additives.