An effective spin-orbital Hamiltonian for the double perovskite SrFeW O: Derivation of the phase diagram
arXiv:cond-mat/0302293 · doi:10.1103/PhysRevB.67.184427
Abstract
We formulate a superexchange theory of insulating double-perovskite compounds such as SrFeWO. An effective spin-orbital Hamiltonian is derived in the strong coupling limit of Hubbard model for d-electrons on Fe and W ions. The relevant degrees of freedom are the spins S=2 and the three-fold orbital degeneracy of Fe-ions. W-sites are integrated out by means of a fourth-order perturbative expansion. The magnetically and orbitally ordered ground states of the effective Hamiltonia n are discussed as a function of the model parameters. We show that for realistic values of such parameters the ground state is antiferromagnetic, as experimentally observed. The order found is of type-II, consisting of \{111\} ferromagnetic planes stac ked antiferromagnetically. The orbital order energy scale found is one order of magnitude less than the spi n one.
12 pages, 4 figures