Analysis of the Coercivity Mechanism of High-Performance Nd-Fe-B Magnets Prepared by Synergistic Diffusion

The grain boundary diffusion process is an important approach for preparing high-performance Nd-Fe-B magnets. In this study, Nd-Fe-B diffusion magnets with both high remanence and high coercivity were prepared via a two-step synergistic diffusion process. The process combined Pr70Ga30 pre-diffusion with subsequent DyH3 diffusion. Compared with DyH3 diffusion alone, this two-step synergistic diffusion strategy increased the coercivity increment from 3.30 to 3.84 kOe while maintaining a remanence of 15.03 kG. Microstructural and elemental analyses showed that Pr70Ga30 pre-diffusion modified the grain-boundary phase and promoted Dy diffusion to greater depths. The modified grain boundaries facilitated the formation of continuous (Dy, RE)2Fe14B shells around the main-phase grains. These shells increased the local magnetocrystalline anisotropy and strengthened the grain edges against reverse-domain nucleation. Micromagnetic simulations indicated that a complete core-shell structure increased the demagnetization nucleation field at grain edges, thereby suppressing magnetic domain reversal. This study establishes a direct relationship between grain-boundary modification, shell continuity, and coercivity enhancement in Nd-Fe-B magnets.