ONE-DIMENSIONAL PHYSICS IN ORGANIC CONDUCTORS (TMDTDSF)2X, SUSCEPTIBILITY AND SE-77-NMR EXPERIMENTS

We present an analysis of spin susceptibility and Se-77 nuclear relaxa tion data for two members of the mixed S-Se series (TMDTDSF)2X, X=ReO4 and PF6. For both compounds, the temperature dependence of the relaxa tion enhancement (TT1)-1 follows, in the paramagnetic regime, the squa re of the temperature dependent uniform static susceptibility measured separately both by ESR and Faraday balance techniques. Then a phase t ransition driven by anion ordering is evidenced for the ReO4 salt. How ever, deviations from the high temperature behaviour are visible in th e PF6 salt below the charge localisation temperature and are explained in terms of antiferromagnetic correlations. The scaling theory for th e quasi-one-dimensional (Q-1-D) electron gas model accounts very well for the NMR behaviour of these mixed molecule systems.