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

Abstract

For the purpose of enhancement of coercivity (H-c) in sintered Nd-Fe-B magnets, we study the effects of high magnetic fields of up to 140 kOe applied during the annealing. We investigated the annealing temperature (T-a) dependence of H-c 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 T-a = 500 degrees C or 550 degrees C. DSC measurements suggest that these temperatures can be interpreted as the eutectic points of Nd70Cu30 and Al17Cu83 phase, respectively. Temperature dependence of H-c and maximum energy product (BH)(max) in the coercivity-enhanced samples were measured up to 250 degrees C. We have found that a sample with H-c = 14.6 kOe at 20 degrees C gives a twice larger (BH)(max) value at 125 degrees C as compared with those in the sample with H-c = 9.8 kOe at 20 degrees C.