The spin-polarised electronic band structure of chromium spinels. II. CuCr₂Se₄and CuCr₂Te₄

Abstract

For pt.I see ibid., vol.15, p.2613 (1982). The electronic band structures of ferromagnetic chromium spinels CuCr2Se4 and CuCr2Te4 are calculated self-consistently by using the discrete variational X alpha method. The main features of the band structure are almost common among the three compounds CuCr2X4 for X=S, Se and Te: relatively narrow valence bands constructed mainly from the anion p orbitals lie in a lower energy region. Very narrow bands having mainly d character range over the intermediate energy region; a few d bands cross the Fermi level for both spin bands of the selenide and telluride while d bands with the majority spin only cross the Fermi level for the sulphide. Wide conduction bands composed of Cu and Cr 4s, 4p orbitals lie in the higher energy region. The valency of each ion obtained from the self-consistent calculation are Cu1.25+(Cr1.41+)2(Se1.02-)4 and Cu0.85+(Cr1.03+)2(Te0.73-)4, which are compared with Cu1.30+(Cr1.55+)2(S1.11-)4. The atomic spin-polarisations of Cr, Cu and X are +3.54, -0.26 and -0.36 respectively for CuCr2Se4, and +3.74, -0.19 and -0.48 for CuCr2Te4. (They were +3.20, -0.32 and -0.27 for CuCr2S4 by way of comparison.).