Effect of Nd-Ho-Al-Ga diffusion on coercivity and thermal stability of hot-deformed PrNd-Fe-B magnets

In this study, to enhance the coercivity and high-temperature stability of hot-deformed PrNd-Fe-B magnets, the NdHoAlGa alloy was utilized as a diffusion source and a dual-alloy diffusion process was employed to enhance the room temperature coercivity from 1.72 to 2.28 T. For the magnet doped with 7 wt% Nd72.3Ho13.8Al2.3Ga11.7, within the temperature range from 20 to 200 °C, the remanence temperature coefficient α increases from −0.16 %/°C to −0.14 %/°C, and the coercivity temperature coefficient β increases from −0.49 %/°C to −0.43 %/°C. By controlling grain boundary (GB) phases and optimizing the main phase simultaneously, Ga was induced to motivate the formation of non-ferromagnetic GB phases, reducing the size of grains and intergranular exchange coupling. Additionally, Ho was diffused into the main phase, forming (Pr,Nd,Ho)-Fe-B phase, which enhances the magnetic crystalline anisotropy field of the main phase grains at high temperatures.