Excellent intrinsic magnetic properties in the TbCu7-type Sm-Fe-N compound

We report excellent intrinsic magnetic properties of SmFe9Nδ (δ=0, 0.5, 0.7 and 1.1) epitaxial thin films with TbCu7-type crystal structure, i.e., room temperature saturation magnetization (μ0Ms) of 1.64 T, Curie temperature (Tc) of 771 K and magnetic anisotropy field (μ0HA) of ~22 T for δ=1.1 the saturation magnetization of which is superior to that of Sm2Fe17N3 (μ0Ms= 1.57 T) and Nd2Fe14B compounds (μ0Ms= 1.61 T). X-ray diffraction and transmission electron microscopy revealed that the thin films have a highly textured single TbCu7-type phase with its c-axis perpendicular to the film. Heat treatment of the thin films under N atmosphere expands the lattice and increases the unit cell volume of the SmFe9Nδ structure, which also switches the magnetocrystalline anisotropy from easy plane (δ = 0) to easy axis (δ=1.1). Furthermore, the μ0Ms and Tc of SmFe9Nδ films also increased with increasing nitrogen content in the structure, leading to promising intrinsic magnetic properties. Based on this study, we can conclude that the rare-earth lean SmFe9Nδ based TbCu7-type compound has potential for the development of high performance anisotropic bonded magnets with superior performance to that of existing anisotropic Sm2Fe17N3 or Nd-Fe-B bonded magnets.