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TT: Fachverband Tiefe Temperaturen
TT 20: Correlated Electrons - Poster Session
TT 20.28: Poster
Mittwoch, 28. März 2007, 14:00–17:45, Poster A
Anion ordering transition in organic quantum spin chains (TMTTF)2X investigated by ESR and SQUID — •Shadi Yasin, Belal Salameh, Michael Dumm, and Martin Dressel — 1. Physikalisches Institut, Universität Stuttgart, Germany
The organic charge-transfer salts (TMTTF)2X are S=1/2 quantum spin chains. The low temperature physical properties of these materials depend strongly on the size and shape of the counter-anion X. Species with non-centrosymmetric anions like ReO4, BF4, and SCN show an anion-order transition at 40 K < TAO < 160 K. This breaking of the inversion symmetry of the molecular conductors has strong impact on the spin and charge degrees of freedom. We investigated the nature of the anion-ordered ground state by temperature dependent ESR and SQUID experiments. We found that the temperature dependence of the ESR linewidth and the spin susceptibility changes drastically below TAO in the compounds with X = ReO4 and BF4 where a spin gap Δσ opens in the non-magnetic anion-ordered ground state. Contrary, in (TMTTF)2SCN the ESR linewidth and the spin susceptibility show only a shallow change below TAO. This is an indication that anion order is accompanied by charge order but not by spin order.