Boundary structure modification and magnetic properties of Nd-Fe-B sintered magnets by co-doping with Dy2O3/S powders

Abstract

In this paper, the effect of Dy2O3/S co-doping on the magnetic properties and microstructure was studied in Nd-Fe-B sintered magnets. With S co-doping, the coercivity increased due to grain boundary modification and Dy selective introduction. Continuous grain boundary phases were formed in the co-doped magnets with smaller grain size. The average grain size after a doping of 0.2wt% S is 7.25µm, which is approximately 2.37µm smaller than that of the S-free sintered magnets(9.62µm). The coercivity of the Dy2O3/0.2wt% S co-doped magnets could be increased from 20.9 to 22.8kOe with changing the remanence and the maximum magnetic energy product slightly. S precipitates in the Nd-rich phases were hexagonal Nd2O2S phase. Dy avoided the Nd2O2S phase in the triple junction region, resulting in more available Dy atoms diffusing into the Nd2Fe14B phase grains to enhance the anisotropy field. Dy-saving was achieved by forming Nd2O2S phase in the Dy2O3/S co-doped magnets.