Magnetic impurity bands in Gax−1MnxS: Towards understanding the anomalous spin-glass transition

We report on magnetic and electronic properties of a quasi-2D single-crystalline Ga0.91Mn0.09S diluted magnetic semiconductor (DMS) that shows an anomalously high spin-glass Tc at 11.2 K. Using density functional theory (DFT), we characterize the properties contributing to the spin-glass transition through an examination of electronic and magnetic properties for Ga1−xMnxS (0<x<0.18). The Mn produces impurity bands in the electronic structure, where an analysis of the density of states shows an increase in magnetic impurity bands at the Fermi level that lowers the semiconducting gap consistent with DMS. This is similar to other DMS, where the primary mechanism is likely through magnetic exchange. The increased electron density with Mn doping could explain the anomalously higher Tc in Ga0.91Mn0.09S. In comparison with the substantially lower transition temperatures in related II-VI based systems (e.g., Zn1−xMnxTe), the high Tc is associated with more metallic spin-glass systems that interact through RKKY exchange, which leads to the conclusion that there may be a combination of interactions occurring in these systems.