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

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.