From positive to negative magnetoresistance behavior at low applied magnetic fields for polyaniline:titania quantum dot nanocomposites

摘要

Here, we report the tuning from the positive to negative magnetoresistance response at room temperature and low applied magnetic fields (H ~ 200 mT) for polyaniline nancomposites prepared via in situ growth of titanium oxide quantum dots. In addition, we showed experimental Raman evidence revealing that the positive magnetoresistance response in these polyaniline nanocomposites is mediated by the bipolaron mechanism. Confocal Raman spectroscopy under applied magnetic field analysis showed the decrease of the polaron population to form bipolarons of polyaniline when exposed to an applied magnetic field for the TiO_2 quantum dot diluted regime. Negative magnetoresistance, observed for the TiO_2 quantum dot higher concentration regime, was attributed to the suppression of polyaniline polarons probably associated with its partial chemical functionalization at the interface due to the increasing concentration of TiO_2 quantum dots.