Europhys. Lett., 61 (6) , pp. 803-809 (2003)
Orbital and spin exchange inA.-M. Daré1, R. Hayn1 and J.-L. Richard2
1 Laboratoire Matériaux et Microélectronique de Provence, UMR 6137, Bât. IRPHE Château Gombert - 49 rue Joliot Curie, BP 146, 13384 Marseille Cedex 13, France
2 Centre de Physique Théorique - Luminy Case 907, 13288 Marseille Cedex 9, France
(Received 8 July 2002; accepted in final form 24 December 2002)
We derive an effective orbital and spin exchange Hamiltonian using a perturbative approach to study the compound . We show that the inclusion of the trigonal crystal field splitting at the oxygen sites leads to the appearance of antiferromagnetic exchange integrals in deviation from the Goodenough-Kanamori-Anderson rules for this 90 degree bond. That gives a microscopic foundation for the recently observed coexistence of ferromagnetic and antiferromagnetic couplings in the orbitally frustrated state of (F. REYNAUD ET AL. Phys. Rev. Lett. 86 (2001) 3638).
71.27.+a - Strongly correlated electron systems; heavy fermions.
75.10.Dg - crystal field theory and spin Hamiltonians.
75.30.Et - Exchange and superexchange interactions.
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