Fe2P based alloys as possible rare-earth free permanent magnets

Abstract

The Fe${}_2$P alloy exhibits high saturation magnetization, large uniaxial magnetic anisotropy, 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. Herein, using systematic theoretical and experimental investigations, it is demonstrated that multi-element substitutions of Co for Fe, and Si and B for P site (among 3$d$ and 2$p$-3$p$ 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 Fe${}_2$P and (Fe,Co)${}_2$(P,Si) alloys. These results suggest a venue for significant advances in the development of permanent magnetic materials based on the Fe${}_2$P-type structure.