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.