High-Tc ferromagnetism in p-type ZnO diluted magnetic semiconductors

Using effective field theory, with a Honmura-Kaneyoshi differential operator technique, the transition temperature as a function of the carrier (hole) n(c) and impurity n(i) concentrations has been obtained for p-type ZnO diluted magnetic semiconductors. The Hamiltonian we used contains a damped and undamped Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction model to describe the exchange coupling constants J(ij) between the local moments Mn-i and Mn-j. We use a higher value of l (undamped RKKY) in order to study the long-range RKKY coupling, and a small value of l (damped RKKY) in order to study the short-range RKKY coupling. By band structure calculation we include the finite band splitting, Delta, in our calculation, and we have calculated the exchange constants N-0 beta for different impurity n(i) and hole n(c) concentrations. We calculated the band gap of Zn1-xMnxO (0 <= x <= 0.5) and Zn0.8Mn0.2O1-yNy (0 <= y <= 0.2), which mimics an optical transmission measurement. The magnetization variation as a function of temperaturefor different hole concentrations and n(c)/n(i) ratios is also investigated. (C) 2009 Elsevier B.V. All rights reserved.