Role of conduction-electron–local-moment exchange in antiferromagnetic semiconductors: Ferrons and bound magnetic polarons

We present a theoretical description of the influence of conduction-electron--local-moment exchange on the properties of free carriers in antiferromagnetic semiconductors, with explicit application to EuTe. We conclude that the ferron, an electron self-trapped in a potential well formed by exchange-induced ferromagnetic polarization of the matrix, does not exist at low temperatures in real three-dimensional antiferromagnets, though it is stable in quasi-one-dimensional systems. An electron bound to a donor site induces a ferromagnetic moment near the donor, and we find that such bound magnetic polaron states account for the ferromagnetic clusters attributed to ferrons in previous studies.