Tuning Fe2Ti Distribution to Enhance Extrinsic Magnetic Properties of SmFe12-Based Magnets

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.