Origins analysis of coercivity enhancement mechanism in diffusion-processed Nd-Fe-B magnets

The Nd13.5Fe79.5B7 bulk magnets were prepared by melt-spinning followed by hot-compaction and post-annealing. In the optimized benchmark magnet, the diffusion process was carried out by using La70Cu30, Nd70Cu30 and Dy70Cu30 alloy powders. Elementary distribution showed that Nd was coexistent with La but immiscible with Dy in the grain boundary (GB) regions. Crystallized GB phase was observed. The components of coercivity enhancement contributed from ferromagnetic decoupling, remedied grain surface and magnetically hardened grain surface were analyzed. Our results demonstrated that remedied grain surface and magnetically hardened grain surface contribute mostly to the enhanced coercivity, instead of ferromagnetic decoupling.