Coercivity Enhancement of Sintered Nd-Fe-B Magnets by Grain Boundary Diffusion with DyH₃ Nanoparticles

Grain boundary diffusion technique with DyH₃ nanoparticles was applied to fabricate Dy-less sintered Nd-Fe-B permanent magnets with high coercivity. The magnetic properties and microstructure of magnets were systematically studied. The coercivity and remanence of grain boundary diffusion magnet were improved by 60% and reduced by 7% compared with those of the original magnet, respectively. Meanwhile, both the remanence temperature coefficient (α) and the coercivity temperature coefficient (β) of the magnets were improved after diffusion treatment. Investigation shows that Dy is preferentially enriched as (Nd, Dy)₂Fe 14 B phase in the surface region of the Nd₂Fe 14 B matrix grains indicated by the remarkable enhancement of the magneto-crystalline anisotropy field of the magnet. As a result, the magnet diffused with a small amount of Dy nanoparticles possesses enhanced coercivity without remarkably sacrificing its magnetization.