Crystal structure,\nChemical Bonding, and Magnetism\nof α‑Fe<sub>6</sub>Ga<sub>5</sub>: How Local Interactions\nShape the Structure and Properties of Intermetallic Compounds

α-Fe<sub>6</sub>Ga<sub>5</sub> was synthesized\nfrom the elements\nas a polycrystalline powder. Its crystal structure was redetermined\nby high-resolution powder X-ray diffraction, which showed a complex\nmonoclinic structure of the Fe<sub>6</sub>Ge<sub>5</sub> type. The\ndetermined lattice parameters (<i>a</i> = 10.08380(6) Å, <i>b</i> = 7.97071(5) Å, <i>c</i> = 7.70489(5) Å,\nand β = 108.3062(2)°) differ notably from the previous\nreports. Despite possessing the same structure type as Fe<sub>6</sub>Ge<sub>5</sub>, α-Fe<sub>6</sub>Ga<sub>5</sub> displays several\ndistinctive features, such as short Ga–Ga bonds and distorted\nFe layers. According to magnetization measurements, α-Fe<sub>6</sub>Ga<sub>5</sub> is a soft ferromagnet with a high Curie temperature\nof 760 K, which is in stark contrast to the antiferromagnetic behavior\nof Fe<sub>6</sub>Ge<sub>5</sub> reported in the literature. The electronic\nstructure of α-Fe<sub>6</sub>Ga<sub>5</sub> was studied theoretically\nusing density functional theory-calculations, which showed the pronouncedly\ncovalent character of the short Fe–Ga and Ga–Ga bonds.\nSimilar calculations were performed for Fe<sub>6</sub>Ge<sub>5</sub>, which revealed stronger Fe–Ge interactions, which preclude\nthe formation of short Ge–Ge bonds. In both cases, the theoretical\ncalculations showed ferromagnetic instability, which leads to ferromagnetic\nordering only in the case of α-Fe<sub>6</sub>Ga<sub>5</sub>,\nlikely due to the different nature of Fe–Ga–Fe and Fe–Ge–Fe\nsuperexchange interactions.