Electronic structure and evidence for La vacancies in the misfit layer compound (La1-xS)(1.20)CrS2

Ab initio spin-polarized band structure calculations using the LSW method were performed for an incommensurate misfit layer compound (LaS)(1.20)CrS2 in the supercell approximation. The electronic structure of (LaS)(1.20)CrS2 can be regarded as that of LaS intercalated into the host CrS2. There is a transfer of 1.2 electrons per Cr from the LaS to the CrS2 layers, La is therefore trivalent. The S 3p orbitals of the LaS subsystem are fully occupied by electrons while there are some unoccupied S 3p states of the CrS2 layers, which indicates covalent interaction between the S and Cr atoms in the CrS2 subsystem. The Cr 3d states are almost completely spin-polarized and the magnetic moment is 3.2 mu(B) per Cr. The energy gap between the valence band (mainly S 3p) and the conduction band (Cr 3d band) is similar to 0.4 eV for spin-up electrons and similar to 1.0 eV for the spin-down electrons. There are 0.2 electrons per Cr in the t(2g) conduction band for the spin-up direction while the Fermi level is in the forbidden gap for the spin-down electrons. Therefore, the calculations indicate that (LaS)(1.20)CrS2 is a so-called half-metallic compound. The presence of La vacancies in(La1-xS)(1.20)CrS2 is discussed. (C) 1997 Elsevier Science Ltd. All rights reserved.