Polaron-polaron interactions in diluted magnetic semiconductors

The bound magnetic polarem (BMP) is the characteristic collective state of diluted magnetic semiconductors. Isolated BMP are well understood, but their interactions are only beginning to be explored. Recent polaron magnetization experiments on p-ZnMnTe suggest a ferromagnetic polaron-polaron interaction, in contrast to the invariably antiferromagnetic impurity exchange interaction in conventional semiconductors. To investigate this question theoretically, we have developed a simplified model of polaron pairs whose central feature is competition between the usual, antiferromagnetic, virtual-hopping interaction, and the loss of carrier-magnetic ion exchange energy, by intermediate ions, when the polaron moments are antiferromagnetically aligned. The model is sufficiently simple that its partition function can be calculated in detail. With reasonable parameters, it predicts a ferromagnetic polaron-polaron interaction at low temperatures.