Theory of ferromagnetism driven by superexchange in dilute magnetic semi-conductors

¹ Physics Department, University of Athens, GR-15784 Athens, Greece
² Institute of Theoretical Physics, Faculty of Physics, University of Warsaw, PL-00 681 Warszawa, Poland
³ Institute for Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems, NCSR Demokritos, GR-15310 Athens, Greece
⁴ Institute of Physics, Polish Academy of Sciences, PL-02 668 Warszawa, Poland
⁵ WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

^a e-mail: csimseri@phys.uoa.gr

Published online: 3 July 2014

Abstract

Magnetic properties of Ga_1−xMn_xN are studied theoretically by employing a tight binding approach to determine exchange integrals J_ij characterizing the coupling between Mn spin pairs located at distances R_ij up to the 16th cation coordination sphere in zinc-blende GaN. It is shown that for a set of experimentally determined input parameters there are no itinerant carriers and the coupling between localized Mn³⁺ spins in GaN proceeds via superexchange that is ferromagnetic for all explored R_ij values. Extensive Monte Carlo simulations serve to evaluate the magnitudes of Curie temperature T_C by the cumulant crossing method. The theoretical values of T_C(x) are in quantitative agreement with the experimental data that are available for Ga_1−xMn_xN with randomly distributed Mn³⁺ ions with the concentrations 0.01 ≤ x ≤ 0.1.