Bound magnetic polaron in semimagnetic semiconductors : Effects of Mn-Mn exchange interaction

Abstract

We study the effects of the antiferromagnetic Mn-Mn exchange interaction on a bound magnetic polaron (BMP) in dilute systems like Cd 1−xMn xTe. The density matrix expansion method is used to show that at high T the magnetic binding energy is proportional to 1 (T + τ) , where τ is smaller than the Curie-Weiss temperature. We discuss the relevance of this result to the usually employed “antiferromagnetic temperature” T 0 and experimental data indicating that (T 0) BMP < (T 0) magnetization. We next consider the low temperature limit and examine the approximation of using a reduced effective concentration ( x ). Finally, a quantum mechanical cluster model is used for studying the effects of increasing average Mn-Mn interaction on the binding energy versus temperature curve of an acceptor BMP. As the magnitude of the interaction increases, the low temperature binding energy decreases and the BMP effect gradually disappears in favour of a magnetic fluctuation-dominated behaviour.