Boniface P. T. Fokwa

The quinary members in the solid solution Hf 2 Fe 1− δ Ru 5− x Ir x + δ B 2 ( x =1–4, VE=63–66) have been investigated experimentally and computationally. They were synthesized via arc‐melting and analyzed by EDX and X‐ray diffraction. Density functional theory (DFT) calculations predicted a preference for magnetic ordering in all members, but with a strong competition between ferro‐ and antiferromagnetism arising from interchain Fe−Fe interactions. The spin exchange and magnetic anisotropy energies predicted the lowest magnetic hardness for x =1 and 3 and the highest for x =2. Magnetization measurements confirm the DFT predictions and demonstrate that the antiferromagnetic ordering ( T N =55–70 K) found at low magnetic fields changed to ferromagnetic ( T C =150–750 K) at higher fields, suggesting metamagnetic behavior for all samples. As predicted, Hf 2 FeRu 3 Ir 2 B 2 has the highest intrinsic coercivity ( H c =74 kA/m) reported to date for Ti 3 Co 5 B 2 ‐type phases. Furthermore, all coercivities outperform that of ferromagnetic Hf 2 FeIr 5 B 2 , indicating the importance of AFM interactions in enhancing magnetic anisotropy in these materials. Importantly, two members ( x =1 and 4) maintain intrinsic coercivities in the semi‐hard range at room temperature. This study opens an avenue for controlling magnetic hardness by modulating antagonistic AFM and FM interactions in low‐dimensional rare‐earth‐free magnetic materials.