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An effective spin-orbital Hamiltonian for the double perovskite Sr$_2$FeW O$_6$: Derivation of the phase diagram

S. Di Matteo·G. Jackeli·N. B. Perkins
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Abstract

We formulate a superexchange theory of insulating double-perovskite compounds such as Sr$_2$FeWO$_6$. 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$^{2+}$-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.

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S. Di Matteo, G. Jackeli, N. B. Perkins. 2003-02-14. An effective spin-orbital Hamiltonian for the double perovskite Sr$_2$FeW O$_6$: Derivation of the phase diagram. https://doi.org/10.1103/physrevb.67.184427

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