The structure and magnetic properties were studied for bulk nanocrystalline dysprosium (Dy) metal prepared by spark plasma sintering method. All the as-prepared samples have hexagonal close packed structure. A decrease in grain size results in remarkable changes in magnetic ordering temperature of the nanocrystalline Dy metal. At 5K, the magnetization drops by 3.35%, and the coercive force increases by three times for nanocrystalline Dy compared to those of coarse-grained bulk Dy sample. These results indicate the remarkable influence of the nanostructure on the magnetism of Dy due to finite size effect.

Grain boundary diffusion technique with DyH 3 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) 2 Fe 14 B phase in the surface region of the Nd 2 Fe 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.

The structure and magnetic properties were studied for bulk nanocrystalline SmCo5 sintered magnet produced by spark plasma sintering technique. X-ray diffraction patterns show that the sintered magnet exhibits CaCu5 crystal structures. Transmission electron microscopy (TEM) observation indicates the average grain size of the magnet of about 40 nm. Magnetic measurement shows that the coercivity reaches as high as 2.85 T; the saturation magnetization and the remanence are 0.71 and 0.5 T, respectively. The magnet exhibits good thermal stability with a coercivity of 0.9 T at 773 K and a coercivity coefficient β of −0.15%/K.