Theory of transition temperature of magnetic double perovskites

We formulate a theory of double perovskite compounds such as Sr2FeReO6 and Sr2FeMoO6 which have attracted recent attention for their possible uses as spin valves and sources of spin-polarized electrons. We solve the theory in the dynamical mean-field approximation to find the magnetic transition temperature T-c. We find that T-c is determined by a subtle interplay between carrier density and the Fe-Mo/Re site energy difference, and that the non-Fe same-sublattice hopping acts to reduce T-c. Our results suggest that presently existing materials do not optimize T-c.