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Nickel ferrite nanoparticles were synthesized by Co-precipitation method. The prepared powder was annealed at 500℃, 700℃ and 900℃. XRD analysis was used for composition and structure investigation. The detection and confirmation of the chemical bond in spinel ferrites were investigated by Fourier transmission infrared spectra (FTIR). Also the magnetic properties of the samples were measured by using a vibrating sample magnetometer (VSM). The XRD analysis revealed a pure ferrite phase with high crystallinity. The average crystallite size calculated by Sherrer's equation resulted in variation crystallite size from 9 to 21 nm depending upon the annealing temperature of the samples. FTIR analysis shows the presence of two vibrational bonds between 400-650 cm-1 corresponding to metal-oxygen interaction at tetrahedral and octahedral sites, respectively. Increasing the annealing temperature gave rise to the enhancement of saturation magnetization from 6 to 31emu/gr and the variation of coercivity between 2 and 80Oe.

Ni 0.5 Co 0.3 Cu 0.2 Fe 2 O 4 and Ni 0.5 Co 0.3 Cu 0.2 Fe 2 O 4 /polyethylene glycol (PEG) were synthesized by using the co-precipitation method. The structural, morphological, magnetic, and dielectric properties of the products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), vibrating sample magnetometry (VSM), and Agilent dielectric probing, respectively. XRD analysis confirms the spinel structure of samples with an average particle size of 13 and 21 nm for Ni 0.5 Co 0.3 Cu 0.2 Fe 2 O 4 and Ni 0.5 Co 0.3 Cu 0.2 Fe 2 O 4 /PEG, respectively. FTIR analysis shows the presence of two vibrational bands between 400 and 600 cm −1 corresponding to lattice vibrations in tetrahedral and octahedral sites. FESEM images indicate the formation of nano-sized particles. The results of VSM imply that both samples show a ferromagnetic behavior. The complex dielectric permittivity of the samples was changed after PEG coating. The real part of the permittivity varied from 4.1 to around 5.7 by adding PEG. Adding PEG polymer caused variation in the average crystallite size, lattice constant, and magnetic coercivity.