Enhancing Intrinsic Magnetic Hardness by Modulating Antagonistic Interactions in the Rare-Earth-Free Magnetic Solid Solution Hf₂Fe_1-Ru_5-xIr_{x< /i>+}B₂

The quinary members in the solid solution Hf2Fe1-delta Ru5-xIrx+delta B2 (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, Hf2FeRu3Ir2B2 has the highest intrinsic coercivity (H-c=74 kA/m) reported to date for Ti3Co5B2-type phases. Furthermore, all coercivities outperform that of ferromagnetic Hf2FeIr5B2, 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.