The ThMn₁₂-type SmFe₁₂-based rare-earth permanent magnet has attracted widespread attention due to its excellent intrinsic magnetic properties and high-temperature stability. However, the challenge in realizing continuous non-magnetic or weakly magnetic grain boundary phases equilibrated with the SmFe₁₂ main phase hinders the enhancement in extrinsic magnetic properties of the SmFe₁₂-based permanent magnet, especially for the coercivity. In this work, by controlling the cooling rate, the uniform distribution of paramagnetic Fe₂Ti phases at grain boundaries is achieved in the SmFe₁₂-based alloy ribbon, resulting in a high coercivity of 7.95 kOe. This improvement is attributed to the elimination of the impurity phase within the SmFe₁₂ main phase and the magnetic isolation effect of the grain boundary phase composed of paramagnetic Fe₂Ti, which is directly observed by transmission electron microscopy and further confirmed by micromagnetic simulation. Moreover, first-principles calculations show that the V element can dope into Fe₂Ti and facilitate the transition of its paramagnetic state at room temperature. This study provides new insights into constructing weakly magnetic grain boundary phases for SmFe₁₂-based permanent magnets, offering a novel approach to enhance coercivity.

Here, we report a soft magnetic nanocrystalline alloy with high electric resistivity (ρ) up to 221 μΩ·cm. The (Fe₈₂Si₃B₁₄Cu₁)_100−xCa_x (x = 0, 0.12, 0.36, and 0.6) alloys were prepared by melt spinning. The effects of Ca addition and annealing treatment on the microstructure and properties of the alloys have been investigated. It was found that Fe₈₂Si₃B₁₄Cu₁ alloys without Ca doping contain mainly one nanocrystalline phase of α-Fe, but both α-Fe and Fe₃B nanophases coexist in the as-prepared alloys with relatively high Ca contents (x = 0.36 and 0.6) and annealed Ca co-doped alloys. The presence of Fe₃B nano-crystals leads to high resistivity without significantly reducing the soft magnetic properties. The saturated magnetic induction B_s of (Fe₈₂Si₃B₁₄Cu₁)_100−xCa_x (x = 0, 0.12, 0.36, and 0.6) alloys ranges from 1.75 T to 1.80 T, and the coercivity H_c of annealed alloys shows a tendency to increase with an increase in Ca content. Meanwhile, the resistivity of both as-prepared and annealed alloys increases with increasing Ca content. The as-prepared (Fe₈₂Si₃B₁₄Cu₁)_99.4Ca_0.6 alloy exhibits an excellent combination of soft magnetic properties with ρ = 221 μΩ·cm, H_c = 20.3 A/m, and B_s = 1.57 T. After annealing, these values changed to 158 μΩ·cm, 21.6 A/m, and 1.79 T, respectively. We believe that this work is helpful for developing nanocrystalline soft magnetic alloys for high-frequency applications.