Magnetoresistive polyaniline-magnetite nanocomposites with negative dielectrical properties

Magnetic polyaniline (PANI) polymer nanocomposites (PNCs) reinforced with magnetite (Fe₃O₄) nanoparticles (NPs) have been successfully synthesized using a facile surface initiated polymerization (SIP) method. The chemical structures of the PANI/Fe₃O₄ PNCs are characterized by Fourier transform infrared (FT-IR) spectroscopy. The thermal stability of the PANI/Fe₃O₄ PNCs is performed by thermogravimetric analysis (TGA). Both transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are used to characterize the morphologies of the PANI, Fe₃O₄ nanoparticles (NPs) and the PNCs. X-ray diffraction (XRD) shows a significant effect of the Fe₃O ₄ NPs on the crystallization structure of the formed PANI. The dielectrical properties of these PNCs are strongly related to the Fe ₃O₄ nanoparticle loadings and unique negative permittivity is observed in all the samples. Temperature dependent resistivity analysis from 50 to 290 K reveals a quasi 3-dimension variable range hopping (VRH) electron conduction mechanism for the nanocomposite samples. The PNCs do not show hysteresis loop with zero coercivity, indicating the superparamagnetic behavior at room temperature. The PNCs with 30 wt% Fe₃O₄ NP loading exhibit a larger positive magnetoresistance (MR = 95%) than 53% of the pure PANI.