Phase evolution, microstructure, and improved magnetic properties for off-stoichiometric SmFe₁₂-based alloys

Low rare earth content and high intrinsic magnetic properties make SmFe₁₂-based permanent magnets a potential candidate for NdFeB-based magnets in medium to high temperature environments. However, the easy formation of multiple ferromagnetic intergranular phases limits the preparation of high coercivity magnets. Composition optimization is an indispensable measure for the realization of high-performance magnets. In this work, off-stoichiometric composition design is employed to prepare SmFe₁₂-based alloys. Ti is first introduced to inhibit the precipitation of α-Fe phase, obtaining a high coercivity of 484 kA/m, while the ribbon undergoes a reduction of remanence significantly. After regulating Fe–Co content to 11.5, the remanence recoveries from 0.51 to 0.65 T with a slight increase in coercivity (484–493 kA/m). Finally, Fe content is optimized to further improve magnetic properties, with both coercivity and remanence are improved simultaneously, reaching 509 kA/m and 0.70 T, respectively. Phase evolution, microstructure and their relationship with magnetic properties are investigated in detail. Micromagnetic simulation shows that the increased domain wall pinning effect induced by the refinement of grain size is the main reason for high coercivity. This work provides a feasible compositional design method for the preparation of high performance SmFe₁₂-based alloys.