Innovative multi-layered Fe 3 O 4 -Gr/carbon/polypyrrole nanofiber composite: "a new frontier in dielectric enhancement and EMI shielding"

This study presents the synthesis and comprehensive characterization of an Fe O -Gr/carbon/polypyrrole nanofiber composite, highlighting its morphology as determined through Field Emission Scanning Electron Microscopy (FE-SEM) analysis, which reveals the small rod-like shape of the nano-fibers with an average diameter of 68 nm calculated from Image J software, contributing to a high surface area. X-ray diffraction (XRD) analysis confirms the effective formation of Fe O -Gr nanofibers, graphene, carbon, and polypyrrole (PPy), showcasing distinct crystallographic phases that strengthen the material's magnetic and conductive properties. The impedance plane plot indicates two relaxation processes at low and high-frequency regions from low to high-temperature ranges of 273 K to 363 K, reflecting complex electroactive charge transport dynamics within the nanofiber composite. Dielectric measurements demonstrate a high dielectric constant (up to 10 ) at lower frequencies, with a gradual decrease at higher frequencies, while tangent loss remains below 1 at higher frequencies and increases at lower frequencies with rising temperatures. The MVRH (Mott. Variable Range Hopping) model reveals a localization length of 1.5 Å, indicating localized charge carrier hopping, which contributes to the composite's electrical conductivity. The SPH (Small Polaronic Hopping) model suggests an activation energy of 1.43 eV, consistent with thermally activated charge carrier transport. In accordance with the double-well model, the conductivity plot also confirms the existence of dual relaxation peaks at low and high frequencies. Last but not least, the composite achieves 99.7% absorption and 99.8% attenuation across the x-band frequency range with a total shielding effectiveness (SE ) of 28.4 dB at a thickness of 3 mm.