High field NMR studies of conduction electron dynamics in metallic polypyrrole-PF6

We report measurements of the proton spin-lattice relaxation rate 1/T1 at the frequencies (ω/2π) 0.96 GHz (temperature T = 1.7 −55 K) and 0.38 GHz (1.7 −200 K) in metallic polypyrrole-PF6 doped to ~ 25% PF6. Within a factor of two, T1T is constant over the full temperature range for each frequency. The rate for the lower frequency is 2 – 8 times faster, depending on T. Although the microscopic details do not fit the model for 1D diffusion, the near constancy of T1T is a strong indication that the dominant proton relaxation mechanism is conduction electron motion. An advantage of the high field measurements is that below 15 K, saturation of any local electron moment magnetization eliminates nuclear spin diffusion to paramagnetic centers as a competing relaxation mechanism, leaving only relaxation by translational motion of the electons.