• Mn substitution in CoFe2O4 nanoferrites significantly tunes structural, dielectric, and magnetic properties, with crystallite size decreasing from 55.20 to 31.40 nm as Mn content increases.
• AC conductivity decreases with Mn2+ doping, while dielectric constant and loss increase with frequency, indicating potential for high-frequency storage devices.
• Saturation magnetization, remanence, and coercivity decline with Mn doping, but CoMn0.20Fe1.8O4 exhibits tunable magnetic parameters suitable for magnetic applications.
• The sol–gel auto-combustion method successfully produces single-phase nanoferrites with enhanced performance for high-frequency device applications.