Ab-intitio studies of electronic properties of chalcogenide spinels.

CuCr$_{2}$Se$_{4}$ is a normal chalcogenide spinel which exhibits ferromagnetic properties including a relatively high Curie temperature of 450 K [1] which makes it a promising candidate for use in spintronics devices. Another chalcogenide spinel of enhanced interest for spintronics is CdCr$_{2}$Se$_{4}$ which seems to be a promising ferromagnetic semiconductor for electrical spin injection into III-V device heterostructures [2]. We report first principles calculations of the electronic structure of substoichiometric CuCr$_{2}$Se$_{4-x}$ and Cu$_{x}$Cd$_{1-x}$CrSe$_{4}$ spinels. The calculations were performed using the Vienna ab-initio simulation program (VASP) within the Generalized Gradient Approximation (GGA) of Density Functional Theory (DFT). Our calculations indicate that both Se deficient CuCr$_{2}$Se$_{4-x}$ as well as Cu$_{x}$Cd$_{1-x}$CrSe$_{4}$ show half-metallic behavior over a wide range of $x $with a gap around the Fermi level in the minority density of states. [1] F.K. Lotgering, Solid State Commun. 2 (1964) 55 [2] G. Kioseoglou et al., Nature Materials 3 (2004) 799