The influence of Gallium doping on the magnetic performance and microstructure of Nd-Fe-B sintered magnets

The influence of Gallium (Ga) doping on the microstructure, thermal stability and the magnetic properties of Nd-Fe-B based sintered magnets was investigated in this paper. It is shown that the intrinsic coercivity increases significantly from 12.4 kOe to 19.4 kOe while the remanence decreases slightly from 14.03 kGs to 13.70 kGs when Ga content increases from 0.0 wt% to 0.5 wt%. The thermal stability of the Ga-doped sample is much better than that of Ga-free sample. Temperature coefficient of intrinsic coercivity β @ 20-120 ℃ by doping 0.5 wt% Ga is −0.585 %/K, which is better than that of Ga-free sample (-0.622%/K). It was observed by the microstructures that the addition of Ga can promote the diffusion of Nd and Cu from triple junction phase (TJP) into grain boundary phase while Fe atoms are enriched around TJPs, resulting in continuous grain boundary (GB) phase and reducing the Fe concentration in GB phase. The Curie temperature increases from 583 K to 585 K after doping 0.5 wt% Ga.