Structure and Magnetic Properties of Fe_1.95P_0.8-xSi_0.2B_x Compounds: Pushing Beyond the Orthorhombic Limit

Fe₂P compounds have recently attracted significant attention due to their large anisotropy and magnetization, making them promising candidates as hard magnetic materials. However, their relatively low Curie temperature limits practical applications. Previous studies have shown that substituting Si for P or Co for Fe increases the Curie temperature; however, Si substitution induces a hexagonal to orthorhombic structural transformation, while Co substitution reduces saturation magnetization. This work examines the evolution of the crystal structure and magnetic properties upon B substitutions in Fe_1.95P_0.8-xSi_0.2B_x compounds close to the hexagonal/orthorhombic transformation. We show that B can increase the Curie temperature up to 675 K and the saturation magnetization to 139 A·m²·kg^-1, while preserving the hexagonal structure beyond the limit allowed by Si substitutions only. X-ray diffraction of magnetically aligned powders confirms a uniaxial easy axis along the c axis and significant room-temperature magnetocrystalline anisotropy. The optimization of the intrinsic magnetic properties based on only metalloid substitutions paves the way for further development of this material family as rare-earth-free permanent magnets.