Orbital effects in cobaltites and vanadates

Despina Louca, University of Virginia

The orbital degree of freedom can play a central role in the physics of transition metal perovskite and spinel oxides because of its intricate coupling with other degrees of freedom such as spin and lattice. In this talk two interesting cases will be presented, LaCoO3 and AV2O4, with dynamic and static orbital ordering effects, respectively. In AV2O4 (A=Zn, Cd), the magnetic V ions form a three-dimensional network of corner-sharing tetrahedra. However, due to the orbital degree of freedom the effective dimensionality of the magnetic interactions reduces to one. In LaCoO3, the thermal activation of the Co ions from a nonmagnetic ground state to an intermediate spin state gives rise to orbital degeneracy. This leads to dynamical Jahn-Teller distortions. The implications of the orbital effects to the structural and magnetic properties will be discussed.

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