Nanocrystalline Cu0.90Co0.10Fe2−xCexO4 spinel ferrite with different concentrations of rare-earth element, cerium (Ce), (x = 0.025, 0.05, 0.075, 0.10), have been synthesized via sol–gel auto-combustion rout. XRD patterns reveal that all the samples crystallize in tetragonal structure. The secondary phase (CeO2) is found to be much more prominent at higher Ce concentration. The grain size decreases from 0.57 μm to 0.35 μm. An improved dielectric constant ( \({\varepsilon }_{\text{r}}\) ) value (3700) and low loss (tanδ) value (6) are observed at x = 0.025 indicating its potential usage in capacitor, high-frequency data storage devices, and in the electronics industry. The impact of cation distribution at octahedral sites and the prominent CeO2 peaks at higher Ce concentrations decreases the dielectric constant value and increases the tanδ. The maximum ac conductivity value (9 × 10−3 (Ωm)−1) is exhibited at x = 0.025, which further declines upon Ce doping due to the increased density of grain boundaries and the reduction of hopping ion pairs of Fe3+ \(\rightleftarrows \) Fe2+ and Co2+ \(\rightleftarrows \) Co3+ at octahedral sites. The conduction mechanism of all the ferrites is driven by the correlated barrier hopping (CBH) model as confirmed by the conductivity plot. The Nyquist plot ( \({Z}^{{\prime}{\prime}}\) versus \({Z}^{\prime}\) ) clearly confirms negative temperature coefficient of resistance (NTCR) and non-Debye type of relaxation in the materials. The magnetic (M–H) loop confirms the ferrimagnetic nature of all the samples with increased Hc, Ms and Mr values which favor their usages in high-density magnetic recording, permanent magnets, magnetic storage devices, etc. Thus, the high thermal stability with excellent dielectric, electric, and magnetic properties of Cu0.90Co0.10Fe2−xCexO4 spinel ferrite proves its worth for electronic and magnetic applications.
