Structural, dielectric, morphological and magnetic properties of cobalt-substituted nickel spinel ferrites (Co_xNi_1-xFe₂O₄) nanoparticles

The aim of this research work is to investigate the relaxation behavior of Co²⁺ ion-doped NiFe₂O₄ spinel ferrite nanoparticles for high-frequency devices applications. In this paper, the cobalt-substituted nickel spinel ferrites with formula Co_xNi_1-xFe₂O₄ and having cobalt concentrations (x = 0.0, 0.05, 0.10, 0.15, 0.20) were synthesized through well-known wet chemical route. Both powder as well as the prepared pallets were annealed in a muffle furnace for 6 h at temperature of 600 °C. The X-ray diffraction analysis (XRD) assisted to get the confirmation about the spinel nature of the synthesized nanoparticles. To investigate the crystallite size, the Scherrer formula was chosen, which showed the crystallite size in the range of 21–23 nm. The variations in lattice constant with effect of cobalt concentrations were determined by considering the (311) plane which were found from 8.380 to 8.388 Å. The Fourier transform infrared spectroscopy (FTIR) was used to study the frequency bands at the octa- and tetrahedral sides. The surface morphology of prepared samples was analyzed using the scanning electron (SEM) and transmission electron microscopy (TEM). The variation of all important dielectric properties of interest (complex dielectric constant, dielectric tangent loss, impedance, A.C. conductivity, and electric modulus) as a function of the Al doping concentration were determined in the frequency range between 1 MHz and 3 GHz using electrochemical impedance spectroscopy. The magnetic properties were investigated with influence of cobalt concentrations under the applied magnetic field using the vibrating sample magnetometer (VSM). The results revealed the soft ferromagnetic behavior of the fabricated compound. Finally, the obtained dielectric and magnetic properties propose the prepared materials can be suitable for high frequency and magnetic storage devices.