Half-metallic electronic structures of giant magnetoresistive spinels:Fe1−xCuxCr2S4(x=0.0,0.5,1.0)

Electronic structures of Cr-based chalcogenide spinels ${\mathrm{Fe}}_{1-x}{\mathrm{Cu}}_x{\mathrm{Cr}}_2{\mathrm{S}}_4\mathrm{}(x=0.0,0.5,1.0\mathrm{})\mathrm{}$ are investigated by using the linearized muffin-tin orbital (LMTO) band method in both the local-spin-density approximation (LSDA) and the $\mathrm{LSDA}+U.\mathrm{}$ The LSDA yields the half-metallic electronic structures for $x=0.0,1.0\mathrm{}$ and the insulating electronic structure for $x=\mathrm{0.5.}\mathrm{}$ The $\mathrm{LSDA}+U$ yields the insulating electronic structures for $x=0.0\mathrm{}$ in agreement with experiments. The orbital ordering driven by the on-site Coulomb interaction for $x=0.0\mathrm{}$ is demonstrated based on the $\mathrm{LSDA}+U$ electronic structures. Orbital magnetic moment $M_{\mathrm{orb}}$ is obtained by taking into account the spin-orbit interaction. $M_{\mathrm{orb}}$’s of Fe and Cu in these compounds are found to be very large, reflecting the localized features of $3d$ band electrons. Conduction models for $x=0.0,0.5,1.0\mathrm{}$ are discussed with the schematic energy diagrams incorporating the Jahn-Teller effect and the half-metallic electronic structures.