Theoretical study of the double perovskite Sr₂ FeMO₆(M = Mo, W)

We study the double perovskite Sr₂ FeMO₆ using a tight-binding model with the renormalized perturbation expansion technique. An analysis of the antiferromagnetic (AF) phase shows that the electronic energy remains larger than in the ferromagnetic (F) state but the difference decreases with increasing charge transfer energy. Therefore, with increasing Fe-M charge transfer energy, the transition to the AF state can be easily driven by the superexchange interaction. The F-AF transition in the system Sr₂ FeMo_x W_{1 - x} O₆ vs. doping is also presented.