Spin dynamics in the organic spin - Peierls system MEM(TCNQ) studied using muon-spin relaxation

We report the first muon-spin relaxation study of an organic spin - Peierls system, the linear-chain compound MEM(TCNQ). Our results show a crossover from a Gaussian relaxation to an exponential relaxation as the temperature is lowered below the spin - Peierls transition. We associate this behaviour with the slowing down of the electronic fluctuations resulting from the opening of a gap in the magnetic excitation spectrum.