Spin soliton dynamics and magnetic susceptibility of (DMe-DCNQI)2Li by ESR under pressure

At ambient pressure, a 1/4 filled spin-Peierls system (DMe-DCNQI)2Li shows spin-Peierls transition at Tsp∼65 K, which increases by about 15 K at 10 kbar. Below Tsp, Curie susceptibility emerges. We measured a frequency dependence of ESR line width of Curie spins, and found a quasi-one-dimensional (Q1D) diffusive motion. We propose that the Curie spins are spin solitons as a domain wall spread over several units. The chains with 4N+n units, where N=integer, n=1, 2, or 3, caused by possible structural defects could provide the spin solitons. The average domain size is ∼100 DCNQI molecules deduced from the Curie constant and the extension of domain wall is found to be several units from the frequency dependence of ESR line width at 4.2 K. The diffusion rate of the spin solitons increases with temperature, suggesting a motion of the spin soliton dominated by phonons, which is similar to the neutral solitons in polyacetylene. It was also found that the pressure tends to suppress the spin soliton motion.