Giant Magnetoresistive Phosphoric Acid Doped Polyaniline-Silica Nanocomposites

The phosphoric acid doped conductive polyaniline (PANI) polymer nanocomposites (PNCs) filled with silica nanoparticles (NPs) have been successfully synthesized using a facile surface initiated polymerization method. The chemical structures of the nanocomposites are characterized by Fourier transform infrared (FT-IR) spectroscopy. The enhanced thermal stability of the PNCs compared with that of pure PANI is observed by thermogravimetric analysis (TGA). The dielectric properties of these nanocomposites are strongly related to the silica nanoparticle loading levels. Temperature dependent resistivity analysis reveals a quasi 3-dimensional variable range hopping (VRH) electrical conduction mechanism for the synthesized nanocomposite samples. A positive giant magnetoresistance (GMR) is observed with a maximum value of 95.5% in the PNCs with a silica loading of 20.0 wt% and 65.6% for the pure PANI doped with phosphoric acid. The observed MR is well explained by wave function shrinkage model by calculating the changed localization length (xi), density of states at the Fermi level (N(E-F)), and reduced average hopping length (R-hop). The effects of particle size on the properties including thermal stability, dielectric properties, temperature dependent resistivity, electrical conduction mechanism, and GMR of the nanocomposites are also studied.