Fe2P Based Alloys as Possible Rare-Earth Free Permanent Magnets

The Fe2P alloy exhibits high saturation magnetization μ0Ms, large uniaxial magnetic anisotropy Ku, and excellent thermal stability, which makes it a potential permanent magnet; however, it suffers from relatively low coercivity Hc, and Curie temperature Tc. Herein, using systematic theoretical and experimental studies, it is demonstrated 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 properties and Tc, while retaining its thermal stability. Specifically, Co-low-content Fe1.96Co0.04P1-xSix phases are identified as the most optimal, with μ0Ms of 0.84 T and Hc of 250.6 Oe at room temperature, and Tc of 440 K for x=0.15, which are higher than the corresponding values for Fe2P (0.45 T, 31.1 Oe, and 321 K) and Co-high-content Fe1.82Co0.18P0.85Si0.15 phase (0.76 T, 240.1 Oe, and 461 K) attained in previous experimental studies. More importantly, the additional B substitute is identified to improve Hc value even further up to 1 kOe and Tc up to 546 K, leading to the theoretical energy density product (BH)max of 200 kJ/m3 at room temperature, which is superior to the known rare-earth free permanent magnetic materials. These results suggest a venue for significant advances in the development of rare-earth free permanent magnetic materials based on the Fe2P-type structure.