Magnetite–Polypyrrole Metacomposites: Dielectric Properties and Magnetoresistance Behavior

The conductive polypyrrole (PPy) polymer nanocomposites (PNCs) reinforced with different magnetite (Fe3O4) nanoparticle loadings have been successfully synthesized by using a facile surface initiated polymerization (SIP) method. The scanning electron microscope (SEM) is used to characterize the surface morphology of the as-received Fe3O4 nanoparticles (NPs), pure PPy and Fe3O4/PPy PNCs. The high-resolution transmission electron microscope (HRTEM) is used to observe the nanoparticle dispersion within the polymer matrix. The chemical structure of the PNCs is characterized by Fourier transform infrared (FT-IR) spectroscopy. The thermal stability of the Fe3O4/PPy PNCs is assessed by thermogravimetric analysis (TGA). X-ray diffraction (XRD) results reveal that the addition of NPs has a significant effect on the crystallization of PPy. The switching frequency, at which the permittivity switches from negative to positive, is observed in the synthesized pure PPy and Fe3O4/PPy PNCs. The optical band gap of Fe3O4/PPy PNCs is studied by ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). The Fe3O4/PPy PNCs exhibit no hysteresis loop, indicating the superparamagnetic behavior. Temperature-dependent resistivity indicates a quasi-3-dimensional variable range hopping (VRH) electrical conduction mechanism for the synthesized samples. The positive magnetoresistance (MR) is observed in the synthesized pure PPy at room temperature and analyzed by the wave function shrinkage model. Meanwhile, the negative MR is obtained in the synthesized magnetic PNCs at room temperature and analyzed by the orbital magnetoconductivity theory (forward interference model).