Electronic structures of magnetic semiconductors FeCr2Se4 and Fe0.5Cu0.5Cr2Se4

Abstract

Electronic structures of Cr-based chalcogenide magnetic semiconductors FeCr(2)Se(4) and Fe(0.5)Cu(0.5)Cr(2)Se(4) are investigated by using the full-potential augmented plane wave (FLAPW) band method in both the generalized gradient approximation (GGA) and the GGA+U (GGA incorporating the on-site Coulomb interaction). The GGA band calculation for the Jahn-Teller distorted FeCr(2)Se(4) with monoclinic structure yields an antiferromagnetic (AF) metallic electronic structure. The GGA+U band calculation yields an insulating electronic structure for AF FeCr(2)Se(4) in agreement with experiments. The orbital ordering in FeCr(2)Se(4) driven by the Jahn-Teller and on-site Coulomb interactions is demonstrated based on the GGA+U electronic structures. For ferrimagnetic Fe(0.5)Cu(0.5)Cr(2)Se(4) with a cubic spinel structure, the GGA and the GGA+U yield nearly insulating and insulating electronic structures, respectively. We have also studied the experimental electronic structure of FeCr(2)Se(4) by employing soft x-ray absorption spectroscopy, soft x-ray magnetic circular dichroism and valence-band photoemission spectroscopy. Both calculational and experimental electronic structure studies indicate that the valence states of Fe and Cr ions in FeCr(2)Se(4) are nearly divalent (Fe(2+)) and trivalent (Cr(3+)), respectively.