Effect of Ga addition on the grain boundary phase and magnetic properties of （Nd， Ce）-Fe-B magnets

This study investigates the impact of Ga on the microstructure and magnetic properties in the grain boundary phase of (Nd, Ce)-Fe-B sintered NdFeB magnets. With 0.1% Ga doping, the intrinsic coercivity (H_cj) of the magnet increases from 891.52 kA/m to 1 043.56 kA/m. The addition of trace amounts of Ga increases the proportion of the REFe₂ (RE=Pr, Nd, Ce) phase in the grain boundaries, but lowers the Ce concentration in the REFe₂ phase. As a result, a REFe₂ phase enriched in Pr and Nd but depleted in Ce is formed. This phase absorbs Fe elements in the adjacent two-particle grain boundaries (adjacent main phase grain boundaries). It drives more Ce elements from the grain boundary triangle (TJP) with high Pr, Nd and low Ce concentration into the two-particle grain boundaries of the REFe₂ phase. Consequently, the two-particle grain boundaries become smoother and more continuous. Additionally, doping with Ga reduces the aggregation of rare earth-rich phases and lowers the eutectic melting point at grain boundaries, thereby improving grain boundary wettability. These effects refine the magnetic microstructure, produce smoother and more continuous grain boundaries, strengthen the magnetic decoupling between main phase grains, and ultimately enhance the magnet’s coercivity.