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

Abstract

Magnetic properties of Ga1−xMnxN are studied theoretically by employing a tight binding approach to determine exchange integrals Jij characterizing the coupling between Mn spin pairs located at distances Rij 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 Rij values. Extensive Monte Carlo simulations serve to evaluate the magnitudes of Curie temperature TC by the cumulant crossing method. The theoretical values of TC(x) are in quantitative agreement with the experimental data that are available for Ga1−xMnxN with randomly distributed Mn3+ ions with the concentrations 0.01 ≤ x ≤ 0.1.