Preparation of Sm-Fe-N hard magnetic nanopowder from micron-sized Sm-H and Fe mixed powder

Fine Sm-Fe-N powder with a mean particle diameter of 58 nm was prepared by a low oxygen-induction thermal plasma process (LO-ITP). Sm-H fine powder prepared by a jet mill process and Fe mixed powder were chosen as starting materials. The obtained Sm-Fe alloy had a TbCu ₇ -type crystal structure at temperatures <700 °C but changed to the stable Th ₂ Zn ₁₇ -type structure at temperatures >800 °C. Nitrogen sufficiently diffused into the lattice, and a TbCu ₇ -type Sm-Fe-N nanopowder was obtained. TEM observation revealed single crystals of the synthesized powder. The coercivity of nitrided nanopowder was only 0.16 T at 300 K due to the existence of a large amount of Fe.