A method to improving the coercivity of sintered anisotropic Sm-Fe-N magnets

Highlights: • Bulk anisotropic sintered Sm₂Fe₁₇N₃ magnets were prepared from the submicron-sized Sm₂Fe₁₇N₃ powder by spark plasma sintering. • The 30 wt. % SmCu-added sintered Sm₂Fe₁₇N₃ magnets have a coercivity of 10.3 kOe and a squareness of 45.9%. In this study, bulk anisotropic sintered Sm₂Fe₁₇N₃ magnets were prepared from submicron-sized Sm₂Fe₁₇N₃ powder by spark plasma sintering. The pure sintered Sm₂Fe₁₇N₃ magnets contain high α-Fe content and have a very low coercivity of 4.1 kOe and poor squareness of 7.1%. The SmCu nanoflakes were added as oxygen absorber to provide a low-oxygen sintering condition. The resultant sintered magnets contain low α-Fe content and show a high coercivity of 10.3 kOe. In this SmCu added sintered magnets, the decomposition of Sm₂Fe₁₇N₃ phase was suppressed and SmCu powder was oxidized instead. The experimental results of this study suggest that an addition of suitable high activity oxygen absorber may be effective in preventing the formation of α-Fe precipitates and improving the coercivity in the fabrication of R-TM compounds based nanostructured bulk magnets.