Magnetic resonance in quantum spin chains with competing exchange interactions

Based on a previous review on magnetic resonance in quantum spin chains (Krug von Nidda et al 2010 Eur. Phys. J. Spec. Top. 180 161-89) we report on further development in this field with special focus on transition-metal oxides and halogenides consisting of quasi one-dimensional spin systems, where both intra-and inter-chain exchange interaction may give rise to frustration effects and higher-order anisotropic exchange contributions like the Dzyaloshinskii-Moriya interaction become decisive for the formation of the magnetic ground state. Selected examples show how NMR and ESR contribute valuable information on the magnetic phases and exchange interactions involved: LiCuVO4 with competing nearest neighbour and next-nearest neighbour intra-chain exchange, LiCu2O2 with complex zig-zag chains, and Cs2CuCl4 where the chains form a triangular lattice with the inter-chain interaction weaker but of the same order of magnitude than the intra-chain interaction. The so called paper-chain compound Ba3Cu3In4O12, where each successive pair of CuO4 plaquettes is rotated by 90 degrees with respect to its predecessor along the c-direction like in a paper-chain, provides an interesting topology of frustrated intra-chain exchange interactions. Finally, a few dimer systems are considered.