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

We report measurements of the proton spin-lattice relaxation rate 1/T-1 at the frequencies (omega/2 pi) 0 96 GHz (temperature T = 1.7 - 55 K) and 0.38 GHz (1.7 - 200 K) in metallic polypyrrole-PF6 doped to similar 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.