Influence of disorder on electrical transport and magnetic properties of HCl-doped polyaniline pellets

The electrical conductivity, magnetoconductivity and static magnetisation of pellets of HCl doped polyaniline has been measured in the temperature range 10-300 K and magnetic fields up to 7 T. The deprotonated Pani-HCl is diamagnetic. The as synthesized Pani-HCl shows crossover from diamagnetic to paramagnetic behavior with increasing temperature whereas the nearly fully protonated sample is paramagnetic in the measured temperature range and has an order of magnitude lower electrical conductivity than the as synthesized sample due to an enhanced disorder. The variation of the of the samples with temperature and disorder has been explained by the VRH theory of Fogler, Teber and Shklovskii (FTS) [2004 Phys. Rev. B 69 035413]. The variable range hopping exponents, = 2/5, 1/4 and = 1 which are predicted by FTS theory for three dimensions, together with crossovers between them as a function of disorder and/or T were experimentally obtained. The applicability of the FTS model is also provided by an analysis of the magnetoconductivity and magnetic susceptibility data and relevant features, i.e., electron localisation length, range of energies that contribute to the VRH, and size of the Coulomb gap due to the inconstancy of the density of states for charge excitations.