Investigation of the TbCu₇-type SmFeN Rare-earth Permanent Magnet

Rare-earth permanent magnets are essential for renewable energy and defense technologies, yet leading magnets such as Nd₂Fe₁₄B face critical supply risks due to the scarcity of elements like Dy and Nd. Our study investigates TbCu₇-type SmFe₉N as a Dy/Nd-free alternative, leveraging samarium’s relative abundance in U.S.-based rare-earth deposits and current low cost to strengthen the U.S. rare-earth supply chain. TbCu₇-type SmFe₉N promises higher Curie temperatures, stronger magnetocrystalline anisotropy, and higher saturation magnetization, compared to Nd–Fe–B, making it an attractive alternative to Nd₂Fe₁₄B.

In our work, SmFe powders were synthesized via high-energy ball milling to investigate phase formation and optimize processing for melt-spinning. X-ray diffraction confirms the formation of metastable single-phase TbCu₇-type SmFe₉ structure, while secondary Th₂Zn₁₇ peaks vanish after re-milling. Scanning electron microscopy reveals flake-like morphologies attributed to ductile Fe-rich and brittle Sm-rich phase interactions. Crystallite sizes range from 100–500 nm, forming micron-scale agglomerates. Ongoing work targets eliminating parasitic α-Fe through gravimetric and magnetic separation.

Our results contribute to understanding of phase stability and process control essential for developing high-performance, Dy/Nd-free SmFeN magnets that combine superior magnetic properties with sustainable, U.S.-sourced materials.