Volume 61, Number 6, March 2003
|Page(s)||803 - 809|
|Section||Condensed matter: electronic structure, electrical, magnetic, and optical properties|
|Published online||01 March 2003|
Orbital and spin exchange in
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
Accepted: 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).
PACS: 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
© EDP Sciences, 2003
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