An NMR analysis of magnetic correlations and dimensionality in organic conductors

Abstract

We present an analysis of experimental NMR data for a class of quasi one-dimensional (1D) organic conductors, the Bechgaard salts and their sulfur analogs. The temperature dependence of the nuclear relaxation, T 1 −1, of the sulfur series (TMTTF) 2X supports the existence of 1D antiferromagnetic fluctuations over a wide range of temperatures. Depending on the relative strength of the coupling to the lattice and on the interchain exchange coupling, these correlations evolve towards either a spin-Peierls or a spin density wave phase. We show that the analysis naturally extrapolates to the (TMTSF) 2X family. The stabilization of the insulating magnetic phase at low magnetic field is apparently provided by the antiferromagnetic interchain exchange coupling, just as it is in the sulfur series. This provides a unique T-P phase diagram for both systems where the interplay between 1D correlation effects and interchain exchange coupling plays a crucial role.