RELATIONSHIP BETWEEN THE INTRINSIC-COERCIVITY AND THE PHASES OF ND-(DY)-FE-B SINTERED MAGNETS

Abstract

The magnetic properties of sintered Nd-(Dy)-Fe-B magnets prepared with different annealing conditions have been investigated. Thermomagnetic analysis was carried out on the sintered and annealed Nd-(Dy)-Fe-B magnets in the temperature range of room temperature to 320-degrees-C. The coercivity of gas-quenched Nd14.1Fe78.3B7.6 magnets after annealing for 1 h at temperatures between 600 and 900-degrees-C is higher by 3 kOe than the furnace-cooled one after annealing. Thermomagnetic analysis found that the sintered Nd14.1Fe78.3B7.6 magnet consists of the Nd2Fe14B phase as well as an unknown magnetic phase (A1) with T(c) around 150-degrees-C. The annealed magnets consist of two unknown magnetic phases (A1,A2) and the Nd2Fe14B phase with a T(c) of 150, 240 and 305-degrees-C, respectively. Thermomagnetic analysis also showed that the M(r) value of the A2 phase in the gas-quenched Nd-Fe-B magnet was higher than that of the furnace-cooled one. These results seem to indicate that increase of coercivity is related to the formation of the A2 phase.