Mechanisms underlying the transition to the long-range spin glass state in the layered quasi-2D III-VI diluted magnetic semiconductor Ga1-xMnxS system

Magnetization data of single crystalline Ga_1-xMn_xS (x=0.09) were implemented in Density Functional Theory (DFT) analysis to characterize the complex exchange channels contributing to the spin-glass transition near T_c = 11.2 K. We examine the magnetization, electronic band structure, and density of states for manganese (Mn) doped gallium sulfide (GaS), which is a quasi-two-dimensional semiconductor. For our computer calculations, we start with undoped GaS and progressively add Mn atoms into randomly determined gallium (Ga) lattice sites up to x=0.18. We find the magnetization increases linearly with Mn doping. The presence of magnetic atoms produces impurity bands in the electronic structure. Examination of density of states shows that an increase in magnetic impurity bands seems to lead to the presence of a weak, but noticeable, spin polarization at the Fermi level. This indicates a possible half-metal state due to increased Mn doping. The presence of the impurity bands or half-metal state in Ga_1-xMn_xS provides a likely mechanism for the higher spin-glass transition temperature in Ga_1-xMn_xS compared with the substantially lower transition temperatures in related II-VI based systems such as Zn_1-xMn_xTe.