Fabrication of Cr Diffused Sm₂Fe₁₇N_x Core-shell Magnetic Powders by Reduction-Diffusion Process

Abstract

In this work, Cr diffused Sm₂Fe₁₇N_x core-shell magnetic powders were prepared by reduction-diffusion (RD) process. Sm₂Fe₁₇ coarse, Cr₂O₃ and Sm₂O₃ fine powders were pulverized and mixed by ball milling, and the mixed powder was heat treated following Ca addition. Cr can diffuse into Sm₂Fe₁₇ powder above 875°C in RD process, and the diffusion distance of Cr increased with increase in RD temperature. Cr diffusion distance into Sm₂Fe₁₇ powder was about 1.1-1.2 μm under RD temperature at 875°C for 1.5 h, and the Cr-diffused Sm-Fe core-shell fine powder was obtained. After nitriding and washing, Cr-diffused Sm-Fe-N fine core-shell powder was successfully obtained, and the coercivity and saturation magnetization of the core-shell powder was 855 kA·m⁻¹ and 122 Am²·kg⁻¹, respectively. The saturation magnetization was higher than non-core-shell Sm-Fe-Cr-N powder.