Synthesis, characterization, magnetic and electrical properties of polyaniline/NiFe2O4 nanocomposite

• PANI/NiFe2O4 nanocomposites were synthesized by in situ polymerization of aniline.
• Materials were characterized by XRD, FTIR, SEM, TEM and TGA.
• PANI/NiFe2O4 showed good electrical conductivity and thermal stability.
• Polyaniline coating significantly changes magnetic properties of nickel ferrite.
• Composite exhibits enhanced high frequency microwave absorption compared to NiFe2O4.

Nickel ferrite (NiFe2O4) nanoparticles were prepared using sol–gel technique; while Polyaniline (PANI)/NiFe2O4 nanocomposites were synthesized via chemical oxidative polymerization of aniline monomer (ANI) in the presence of various ferrite amounts (nickel ferrite/ANI = 2.5, 5, 25 and 50 wt%). The morphology, structure, magnetic, electrical and microwave absorption properties of ferrite powders and nanocomposites were characterized by Fourier transform infrared (FTIR), powder X-ray diffraction (XRD), UV–vis absorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), four-point probe resistivity instrument and vector network analyzer. The crystalline size of nickel ferrite was found in the range of 23–27 nm. The results of TGA, FTIR and UV–vis spectra indicated that nickel ferrite particles improved the thermal stability of composite, and there were interactions between ferrite particles and PANI. The nanocomposites under applied magnetic field exhibited the hysteresis loops of ferromagnetic nature at room temperature. The conductivity of all measured samples decreased with decreasing temperature, exhibiting typical semiconductor behavior. The microwave absorbing properties of the nickel ferrite and composite specimens with the coating thickness of 2 mm were investigated using waveguide method in the frequency range of 1–6 GHz. The results showed a microwave absorption band with frequency shifts to the higher frequency region with the increase in PANI content. The maximum reflection loss reaches −12.5 dB at 2.5 GHz for the nickel ferrite and −20.3 dB at 3.78 GHz for the composite containing 95 wt% aniline. The electronic and magnetic properties of the nanocomposites are tailored by controlling the ferrite content.