Electrical and dielectric properties of rare earth substituted hard-soft ferrite (Co0.5Ni0.5Ga0.01Gd0.01Fe1.98O4)x/(ZnFe2O4)y nanocomposites

Abstract ZnFe2O4 (ZFO) NPs (nanoparticles), Co0.5Ni0.5Ga0.01Gd0.01Fe1.98O4 (CNGaGdFO) NPs and hard-soft spinel ferrite (H/S) (CNGaGdFO)x/(ZFO)y (x:y = 1:1, 1:2, 1:3, 2:1, 3:1 and 4:1) NCs (nanocomposites) were synthesized via a one-pot sol–gel auto combustion route. X-ray powder diffraction (XRD) analyses confirmed the purity of ZFO NPs, CNGaGdFO NPs and H/S (H/S) (CNGaGdFO)x/(ZFO)y (x:y = 1:1, 1:2, 1:3, 2:1, 3:1 and 4:1) (absence of any second phase). The crystallite size of NCs was between 39 and 52 nm. The cubic morphology was observed for ZFO NPs, CNGaGdFO NPs and all H/S NCs by the help of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. Energy dispersive X-Ray analysis (EDX) also confirmed the chemical formula of all the NC samples. Electrical and dielectric properties of ZFO NPs, CNGaGdFO NPs and H/S NCs were explored with an impedance analyzer with f ≤ 3.0 MHz, where f stands for frequency, and within the temperature range between 20 and 120 °C. Electric and dielectric parameters such as AC conductivity as well as DC conductivity, activation energy, dielectric constant, dielectric loss in addition to the dissipation parameter relevant to the electrical energy due to different physical processes were measured for each of the given compositional ratios. The AC conductivity was found to follow the frequency-dependent power law in general, being mainly reliant on the compositional ratios and the measured temperatures especially at lower frequencies. This study has shown that CoNiGaGdFeO-ZnFe2O4 H/S NCs carry out conduction mechanisms, which can be predominantly credited to grain–grain boundaries for various compositional ratios. The dielectric constant of (CNGaGdFO)x/(ZFO)y (x:y = 1:1, 1:2, 1:3, 2:1, 3:1 and 4:1) H/S NCs indicates common dielectric behaviours with frequency, largely dependent on compositional rates of the hard to soft spinel ferrites. It is observed that hard ferrite is dominant in the formation of the semicircles, and the diameter of the semicircles shows a drop as the temperature rises, suggesting a temperature-dependent relaxation mechanism. Consequently, the observed variation of the studied dielectric parameters with frequency can be explained by the conduction mechanism in most composition ratios of hard to soft spinel ferrites, which can be explained by a phenomenological method with Koop's model.