Possible impurity-induced ferromagnetism in II-GE-V₂ chalcopyrite semiconductors

Recently reported room-temperature ferromagnetic (FM) semiconductors Cd_1-xMn_xGeP₂ and Zn_1-xMn_xGeP₂ point to a possible important role of II-IV-V2 chalcopyrite semiconductors in "spintronic" " studies. Here, structural, electronic, and magnetic properties of (i) Mn-doped II-Ge-VI2 (II=Zn or Cd and V=P or As) chalcopyrites and (ii) the role of S as impurity in Cd_1-xMn_xGeP₂ are studied by first-principles density functional calculations. We find that the total energy of the antiferromagnetic (AFM) state is lower than the corresponding FM state for all systems with Mn composition x = 0.25, 0.50, and 1.0. This prediction is in agreement with a recent experimental finding that Zn_1-xMn_xGeP₂ experiences a FM to AFM transition for T less than 47 K. Furthermore, a possible transition to the half-metallic FM phase is predicted in Cd_1-xMn_xGeP₂ due to the electrons introduced by n-type S doping, which indicates the importance of carriers for FM coupling in magnetic semiconductors. As expected, the total magnetic moment for the FM phase is reduced by one μ_B with each S substituting P.