Low-energy excitations in the electron-doped metal phtalocyanine LiO.5MnPc from Li and 1H NMR

NMR and magnetization measurements in Li0.5MnPc (Pc=C32H16N8), recently proposed as a strongly correlated metal, are presented. Two different low-frequency dynamics are evidenced. The first one, probed by 1H nuclei, gives rise to a slowly relaxing magnetization at low temperature and is associated with the freezing of MnPc S=3/2 spins. This dynamics is similar to the one observed in pristine beta-MnPc and originates from Li-depleted chain segments. The second one, evidenced by the 7Li spin-lattice relaxation rate, is associated with the hopping of the electrons along Li-rich chains. The characteristic correlation times for the two dynamics are derived, and the role of the disorder is briefly discussed.