<p>Ferrite materials properties can be precisely tailored by adjusting their spinel structure to optimize cation distribution and electronic configuration. Furthermore, doping with various elements significantly enhances their functional qualities. An auto − combustion technique was used to dope nickel ferrite with different Mn²⁺ concentrations, producing the Ni_1−xMn_xFe₂O₄ (<i>x</i> = 0.1, 0.3, and 0.5) nanoparticle series. The crystallite size is compared with Debye–Scherrer, modified Debye–Scherrer, and the W − H plot, and the observations are recorded. The electrochemical investigations revealed a reversible and stable redox behaviour, with distinct potential plateaus indicating oxidation and reduction peaks, and a strong linear correlation (<i>R</i>² = 0.979). Notably, the specific capacitance analysis uncovered an inverse relationship between current density and charge storage capacity, with a maximum specific capacitance of 215 F g⁻¹ at 0.5 A g⁻¹ for NMF-0.5. This sample also showed power and energy density of 125 Wh kg⁻¹ and 14.9 W kg⁻¹, respectively. The electrical properties, such as AC conductivity, was&#xa0;studied using Joncher's power law fitting, with a conductivity of up to 3.37 × 10⁻⁵ S cm⁻¹ and a DC conductivity of 2.0 × 10⁻⁵ S cm⁻¹, highlighting the potential applications of the obtained materials in both low- and high-frequency ranges. The superior performance of this sample is attributed to the synergistic-effects of multivalent states, an exceptional porous structure, and minimal charge transfer resistance.</p>