Ferromagnetism in the Fe-substituted spinel semiconductor ZnGa 2O4

Abstract

Motivated by the recent experimental observation of long range ferromagnetic order at a relatively high temperature of 200 K in the Fe-doped ZnGa2O4 semiconducting spinel, we propose a possible mechanism for the observed ferromagnetism in this system. We show, supported by band-structure calculations, how a model similar to the double-exchange model can be written down for this system and calculate the ground state phase diagram for the two cases where Fe is doped either at the tetrahedral position or at the octahedral position. We find that in both cases such a model can account for a stable ferromagnetic phase in a wide range of parameter space. We also argue that in the limit of high Fe2+ concentration at the tetrahedral positions a description in terms of a two-band model is essential. The two eg orbitals and the hopping between them play a crucial role in stabilizing the ferromagnetic phase in this limit. The case when Fe is doped simultaneously at both the tetrahedral and the octahedral position is also discussed. © 2005 IOP Publishing Ltd.