Crystal structure, Chemical Bonding, and Magnetism of α-Fe6Ga5: How Local Interactions Shape the Structure and Properties of Intermetallic Compounds

α-Fe₆Ga₅ was synthesized from the elements as a polycrystalline powder. Its crystal structure was redetermined by high-resolution powder X-ray diffraction, which showed a complex monoclinic structure of the Fe₆Ge₅ type. The determined lattice parameters (a = 10.08380(6) Å, b = 7.97071(5) Å, c = 7.70489(5) Å, and β = 108.3062(2)°) differ notably from the previous reports. Despite possessing the same structure type as Fe₆Ge₅, α-Fe₆Ga₅ displays several distinctive features, such as short Ga–Ga bonds and distorted Fe layers. According to magnetization measurements, α-Fe₆Ga₅ is a soft ferromagnet with a high Curie temperature of 760 K, which is in stark contrast to the antiferromagnetic behavior of Fe₆Ge₅ reported in the literature. The electronic structure of α-Fe₆Ga₅ was studied theoretically using density functional theory-calculations, which showed the pronouncedly covalent character of the short Fe–Ga and Ga–Ga bonds. Similar calculations were performed for Fe₆Ge₅, which revealed stronger Fe–Ge interactions, which preclude the formation of short Ge–Ge bonds. In both cases, the theoretical calculations showed ferromagnetic instability, which leads to ferromagnetic ordering only in the case of α-Fe₆Ga₅, likely due to the different nature of Fe–Ga–Fe and Fe–Ge–Fe superexchange interactions.