An effective spin-orbital Hamiltonian for Sr₂FeWO₆

We have developed a superexchange theory for the insulating double-perovskite compound Sr₂FeWO₆. The theory has been implemented in an effective spin-orbital Hamiltonian formulated in terms of spin (S = 2) and orbital pseudo-spin (τ = 1) degrees of freedom of the iron ion only, while W-sites have been integrated out by means of a fourth-order perturbative expansion. We have shown that for realistic values of the model parameters the ground state is antiferromagnetic, as experimentally observed.