NMR Analysis of Spin Fluctuations in the Organic Conductor TTF[Ni(dmit) 2 ] 2

We present and analyse 1H NMR relaxation (T1-1) data of the two-chain organic conductor TTF [Ni(dmit)2]2 as a function of temperature and magnetic field at ambient pressure. In the entire temperature domain studied between 1 and 300 K, we report important deviations to the normal metal Korringa law. We show that both T1 temperature and field dependences can be well understood in terms of a typical balance between 1D uniform field-dependent and diffusive spin correlations, which dominate the relaxation enhancement above 60 K or so, and 1D antiferromagnetic fluctuations that strongly develop below this temperature with a power law temperature dependence. The successful comparison between theory and experiment strongly supports a model in which TTF-conducting chains are dominated by repulsive electron-electron interactions and 1D correlation effects down to the lowest temperature reached.