Investigation of Substitution of Nickel Cations in Cobalt Ferrite (CoFe₂O₄) Nanoparticles and Their Influence on Frequency and Temperature Dependent Dielectric and Magnetodielectric Properties

CoFe₂O₄ (CFO) nanoparticles with different contents of Ni (x = 0.0, 0.05, 0.1, 0.15, and 0.2) (CoNi_xFe_(2−x)O₄) were prepared via sol–gel auto combustion method. The structural characteristics of the prepared samples were characterized using room temperature X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), RAMAN. Moreover, the electrical conductivity and magnetic properties of the nanoferrites were investigated using impedance analyzer and vibrating sample magnetometer. Pure CFO and Ni doped CFO showed spinel crystalline structure with presence of secondary phase at higher doping content of Ni. The FESEM micrographs of the nano ferrites showed different aggregations for the different Ni contents and reduction in particle size was obtained with increasing Ni content which was also divulged from the crystallite sizes calculated from XRD data. With Ni substitution, saturation magnetization was found to decrease rapidly. The frequency (100 Hz–1 MHz) and temperature (30–450 °C) dependent dielectric properties show that the dielectric constant is T-independent and at a certain point increasing trend overcomes. Magnetodielectric (MD) studies revealed that the magnetic ordering of Ni doped CFO consequences in the increase in number of polar domains thereby improving the MD effect. The high MD property outcome of this work established the unification of the synthesized samples for multifunctional device applications.