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

The electrical conductivity and static magnetisation of selected own-made HCl-doped polyaniline pellets were measured in the temperature range 10–300 K and in magnetic fields up to 2 T. The deprotonated sample is diamagnetic, the as-synthesised sample exhibits a change from diamagnetic to paramagnetic behaviour as temperature decreases, whereas the fully protonated sample is paramagnetic over the whole temperature range. Furthermore, the fully protonated sample has an order of magnitude lower room temperature conductivity than the as-synthesised sample, which is ascribed to the former being more disordered. Electrical conductivity of the samples as a function of temperature reveals variable-range-hopping exponents 2/5 and 1/4 as well as the nearest-neighbour-hopping exponent 1, which appear in different temperature ranges. These temperature ranges and temperatures of crossovers between them are set by disorder. All the observed exponents and crossovers are in agreement with the Fogler–Teber–Shklovskii model of variable-range-hopping conductivity in three dimensions. This is supported further by an analysis of the magnetisation data, where the above-mentioned crossover temperatures define the energy scale for mechanisms which contribute to the magnetic susceptibility.