Mechanism of Ferromagnetism in Diluted Magnetic Semiconductors at Low Carrier Density.

We analyze critical temperature of ferromagnetic ordering in diluted magnetic semiconductors in the mean-field approximation. Using a general field-theoretical approach we formulate a description of magnetic phase transition, which takes into account the interaction of magnetic fluctuations. We also propose a mechanism of exchange interaction between Mn impurity moments in GaMnAs alloys via the Mn-induced acceptor levels. This mechanism may lead to low temperature ferromagnetism at vanishing concentration of free carriers. [ABSTRACT FROM AUTHOR]