Berlin 2005 – scientific programme

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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.4: Poster

Saturday, March 5, 2005, 11:00–16:30, Poster TU C

Antiferromagnetic Quantum Chain Systems with Competing nn and nnn Interaction — •Reinhard K. Kremer — MPI für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany

Antiferromagnetic (afm) S=1/2 Heisenberg chain systems with uniform nearest-neighbour exchange coupling are best understood. The ground state and the excitation spectrum are well known and the experimental observations are in good agreement with theory. Additional next-nearest neighbour exchange along the chains which can be described by the Majumdar-Ghosh Hamiltonian H=J_nn ∑_i (S_i S_i+1 + α S_i S_i+2) with α=J_nnn/J_nn gives rise to a more complex behaviour, since next-nearest neighbour interaction may lead to magnetic frustration. I review the magnetic properties of the afm S=1/2 Cu²⁺ chain systems LiCuVO₄ and CuX₂ (X=Cl, Br) for which afm incommensurate long-range ordering has been observed by neutron diffraction at low temperatures. The appearance of incommensurate ordering is ascribed to competing nn and nnn exchange interaction which is also evidenced in the bulk magnetic properties.