Ab Initio Study of Electronic and Magnetic Properties of Co-doped AlAs.

First principles calculations were performed to study the electronic and magnetic properties of cobalt doped AlAs within Density Functional Theory formalism. The study was done using a 6.25{\%} Co concentration with a 2\texttimes 2\texttimes 2 supercell. Substitutions of Al or As by Co atoms were done, preferring to replace Al atoms. Total energy calculations for non-magnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM) states were performed. In the supercell two Al atoms were replaced by two Co atoms at different distances (4.051 {\AA}, 5.729 {\AA}, 7.016 {\AA}, 8.102 {\AA} and 9.922 {\AA}) for five different possible configurations: C0-1, C0-2, C0-3, C0-4 and C0-5. C0-n indicates the configuration corresponding to one Co atom placed in the origin and another one placed in n position. For 6.25{\%} Co-doped AlAs, configuration C0-1 results to be more stable in a FM state with a total magnetization of 4 $\mu $B. In this configuration, the impurities are separated by a distance of 3.960 {\AA}, and the smallest distance between Co-As was of 2.356 {\AA}. The dilute magnetic semiconductor prefers the FM state over the AFM by an energy difference of 25 meV.