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RESEARCH PRODUCT

Conduction band polarization in some CMR materials

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First principles electronic structure calculations reveal certain important common features in the conduction band polarization of many of the newly examined colossal magnetoresistance (CMR) materials. Most CMR compounds seem to possess a localized, magnetic band slightly below the Fermi energy. This localized band transfers polarization to a relatively broad conduction band. The nature of the two bands in different systems can be quite distinct. In the perovskite-derived manganese oxides, the magnetic band is derived from $Mn t_{2g}$ states while the conduction band is derived from Mn e states. In the chalcospinel $Fe_{^0.^5}$ $Cu_{^0.^5}$ $Cr_{2}$$ S_{4}$ , the $Crt_{2g}$ states which are below $E _{F}$ polarize conducting Fe d states. In Gd metal and the newly discovered CMR material GdI , the metallic Gd d states are polarized by the 2 underlying f levels. In double perovskites (elpasolites) such as $Sr_{2}$ $FeMoO_{6}$ , Fe states similarly polarize the broader Mo-derived conducting d states. In the pyrochlore $Tl_{2}$ $ Mn_{2}$$ O_{7}$ , localized, magnetic Mn d states polarize the conduction band derived from bonding Tl–O states. In all the systems except Gd metal, the conduction band seems to be strongly spin differentiated. The systematics obtained here provide guidelines for the design of new CMR systems.