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

Abstract

α-Fe 6 Ga 5 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 Fe 6 Ge 5 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 Fe 6 Ge 5 , α-Fe 6 Ga 5 displays several distinctive features, such as short Ga−Ga bonds and distorted Fe layers. According to magnetization measurements, α-Fe 6 Ga 5 is a soft ferromagnet with a high Curie temperature of 760 K, which is in stark contrast to the antiferromagnetic behavior of Fe 6 Ge 5 reported in the literature. The electronic structure of α-Fe 6 Ga 5 was studied theoretically using density functional theorycalculations, which showed the pronouncedly covalent character of the short Fe−Ga and Ga−Ga bonds. Similar calculations were performed for Fe 6 Ge 5 , 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-Fe 6 Ga 5 , likely due to the different nature of Fe−Ga−Fe and Fe−Ge−Fe superexchange interactions.