Preparation of Sm–Fe–N Hard Magnetic Nanopowder From Micrometer-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 (LO–ITP) process. 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 TbCu7-type crystal structure at temperatures $< 700 ^{\circ }\text{C}$ but changed to the stable Th2Zn17-type structure at temperatures $>$ 800 °C. Nitrogen sufficiently diffused into the lattice, and a TbCu7-type Sm–Fe–N nanopowder was obtained. Transmission electron microscopy (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.