Electronic structure and magnetism for FeSi(1-x)Gex from supercell calculations

Recent studies of FeSi(1-x)Gex, which found a transition from an insulating to a magnetic metallic state near x=0.25, have revived the discussion about the role of strong correlation in these systems. Here are spin-polarized band calculations made for 64-atom supercells of FeSi(1-x)Gex for different x and different volumes for large x. The results show that the small band gap in FeSi is closed for x⩾0.3, because of both substitutional disorder and increased volume. Ferromagnetism appears near this composition and becomes enforced for increasing x. The x-dependence of the electronic specific heat can be understood from the exchange splitting of the density-of-states near the gap. Strong volume dependencies for the properties of FeGe suggest experiments using pressure instead of x for investigations of the gap.