Ferromagnetic transition in ordered double perovskites and related alloys

We study the electronic and magnetic properties of ordered perovskites Sr ₂FeMO₆ (where M is a transition metal), among which some compounds, like Sr₂FeMoO₆ are half-metallic with high Curie temperature while Sr₂FeWO₆ is an antiferromagnetic insulator. Using a double exchange type model with an interaction between localized spins and conduction electrons together with a tight-binding Hamiltonian and the renormalized perturbation expansion method, we study the behavior of T_c as a function of the number of conduction electrons and also as a function of the Fe-M energy difference. We also consider the Sr₂FeMo_xW_1-xO₆ compounds which present a magnetic and metal-insulator transition as a function of doping.