Electronic Band Structure of Magnetic Semiconductors with Spinel Structure

Abstract

The electronic band structures of ferromagnetic semiconductors CdCr 2 S 4 , CdCr 2 Se 4 , and HgCr 2 Se 4 are calculated self-consistently by the DV-Xα method. The general features of the band structures are quite similar for three substances except for the relative positions of the 3 d bands: Each structure consists of relatively narrow valence bands, fairly wide conduction bands, and very narrow d bands. The d ε and d γ bands for up-spin lie in the energy region near the top of the valence bands and around the bottom of the conduction bands, respectively, and both d bands for down-spin fall in the conduction bands. The fundamental energy gap at the Γ point is 2.6, 2.3 and 1.8 eV for CdCr 2 S 4 , CdCr 2 Se 4 , and HgCr 2 Se 4 , respectively. The spin polarization of the Cr-3 d orbitals is about 3.5, while the spin polarization of the valence p orbitals of a chalcogen ion has the opposite sign.