Enhancement of coercivity in Al and Cu added Nd-Fe-B sintered magnets by high feld annealing

For the purpose of enhancement of coercivity (Hc) in sintered Nd-Fe-B magnets, we study the effects of high magnetic felds of up to 140 kOe applied during the annealing. We investigated the annealing temperature (Ta) dependence of Hc systematically. Coercivity enhancement phenomena induced by the magnetic annealing were observed only when the sample contains a small amount of Al and Cu additives, and the annealing temperature is in the vicinity of Ta 500°C or 550°C. DSC measurements suggest that these temperatures can be interpreted as the eutectic points of Nd70Cu30 and Al17Cu83 phase, respectively. Temperature dependence of Hc and maximum energy product (BH)max in the coercivity-enhanced samples were measured up to 250°C. We have found that a sample with Hc 14.6 kOe at 20°C gives a twice larger (BH)max value at 125°C as compared with those in the sample with Hc 9.8 kOe at 20°C.