Theoretical and experimental studies of Fe₂P based alloys as possible rare-earth free permanent magnets

The Fe₂P alloy exhibits high saturation magnetization M_s, large uniaxial magnetic anisotropy K_u, and excellent thermal stability, which make it a potential permanent magnet; however, it suffers from relatively low coercivity H_c, and Curie temperature T_c below room temperature. In this presentation, using systematic theoretical and experimental investigations, we report that multi-element substitutions of Co for Fe, and Si and B for P site (among 3d and 2p-3p substitutional elements) enhance permanent magnetic performance, while retaining its thermodynamic stability. Specifically, we find H_c values up to 1 kOe at room temperature and T_c values more than 500 K at a magnetic field of 2 T in (Fe,Co)₂(P,Si,B), leading to the theoretical energy product (BH)_max of 126 kJ/m³ and hardness parameter no less than 1 at room temperature, which are notably larger than the corresponding values for known rare-earth free permanent magnetic materials. These results suggest a venue for significant advances in the development of permanent magnetic materials based on the Fe₂P-type structure.