Thursday, June 25, 2009, 1:30 pm — Small Seminar Room, Bldg. 510
The physics of two the vanadates, CaV2O4 and MgV2O4 will be discussed. Both materials possess the spin-1 magnetic ion, V3+, but have different structures. CaV2O4 consists of quasi-one-dimensional zig-zag chains of V3+ with frustrated first and second neighbour exchange interactions, while MgV2O4 is a spinel where the V3+ lie on a frustrated pyroclore lattice. As well as magnetic degrees of freedom the electronic configuration of V3+ consists of two electrons in the three t2g levels giving rise to orbital degrees of freedom in these compounds. The orbital and magnetic degrees of freedom are strongly coupled because the magnetic interactions occur via direct overlap of the t2g orbitals, as a result orbital ordering has a strong impact on the magnetism. Here we present neutron scattering data of the magnetic structure and excitations which reveal that at high temperatures CaV2O4 behaves as a Haldane chain, but at low temperatures, it is a spin-1 ladder, while MgV2O4 show one-dimensional behaviour at low temperatures. The results are discussed in term of orbital ordering.
Hosted by: Alexei Tsvelik
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