Mn-dopedCuGaS2chalcopyrites: Anab initiostudy of ferromagnetic semiconductors

Abstract

Stimulated by our recent findings suggesting that the $\mathrm{I}-\mathrm{III}-{\mathrm{VI}}_2$ chalcopyrites could be a different class of ferromagnetic semiconductors, we performed first-principles calculations within density-functional theory and the generalized gradient approximation for Mn-doped ${\mathrm{CuGaS}}_2.$ Our calculations confirm the previous theoretical predictions on ${\mathrm{CuGaSe}}_2,$ that the ferromagnetic spin configuration is strongly favored. Mn is found to be, as expected, both a source of localized magnetic moments and an acceptor; thus, our results seem to support the general idea that ferromagnetism is stabilized through a carrier-mediated interaction. For all the systems, we find a half-metallic character, consistent with the integer value of the total magnetic moment of $4{\mu }_B$ per Mn atom. This is particularly important for spin-injection applications: in a significant energy range (i.e., about 0.5 eV in the dilute case) around the Fermi level relevant for spin injection, the holes will have a well-defined spin. A simple Heisenberg model to estimate the Curie temperature $T_c$ in ordered ${\mathrm{CuMn}}_x{\mathrm{Ga}}_{1-x}{\mathrm{S}}_2$ alloys gives $T_c\sim 160\mathrm{K},$ therefore suggesting the possible importance of this class of ferromagnetic semiconductors for spintronic applications.