Effect of temperature and magnetic field on the electrical transport of polyaniline nanofibers

The detailed nature of conduction in polyaniline nanofibers has been studied as a function of temperature as well as magnetic field. Three batches of nanofibers doped with different levels of hydrochloric acid are synthesized by interfacial polymerization technique with an average diameter of 7.5 nm. The structural studies show an increase in crystallinity with doping while the Raman spectroscopy reveals polaron as the major charge carrier. All the samples show a metal-insulator transition around 16K. At low temperature, the metallic conduction has been ascribed to electron-electron interaction effects while in the high temperature insulating regime, the conduction mainly occurs by variable range hopping mechanism among superlocalized states. All the materials exhibit a sizable amount of magnetoresistance at all temperatures. It is, however, intriguing that the nature of magnetoresistance changes from positive to negative with temperature, and the magnitude of magnetoresistance itself modifies with the doping concentration. We have qualitatively explained this behavior of magnetoresistance with a polaron-bipolaron based model. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793588]