Frequency-Dependent Dielectric Response, Enhanced Electrical Resistivity, and Magnetic Tunability in Ti4+-Mn2+ co-doped CoFe₂O₄ Nanoparticles Synthesized via Sol-gel Method.

The Ti ⁴⁺ -Mn ²⁺ co-doped cobalt ferrite nanoparticles, CoFe _2-2x Ti _x Mn _x O ₄ (x = 0.00, 0.05, 0.10, 0.15, and 0.20), were synthesized via the sol-gel auto-combustion method to investigate their structural, magnetic, electrical, and dielectric properties. X-ray diffraction confirmed a single-phase cubic spinel structure for all compositions, with lattice constants increasing with doping concentration (x), attributed to ionic radius disparities between substituted (Ti ⁴⁺ , Mn ²⁺ ) and host (Co ²⁺ , Fe ³⁺ ) ions. Scherrer’s analysis revealed crystallite sizes (nanoscale: ~17–24 nm), consistent with nanocrystalline morphology. SEM images displayed spherical grains with an average size of 50–80 nm with moderate agglomeration. FTIR spectra exhibited characteristic absorption bands near 600 cm ^-1 and 400 cm ^-1 , affirming the spinel framework. Magnetic properties, including saturation magnetization (45–60 emu/g) and magneton number, exhibited non-monotonic trends with doping, likely due to cation redistribution and spin canting. DC resistivity increased with x, linked to reduced electron hopping between Fe ²⁺ and Fe ³⁺ ions as Ti ⁴⁺ and Mn ²⁺ occupied octahedral sites. Dielectric parameters (permittivity, loss tangent) decreased with rising frequency 1 kHz-1 MHz, typical of Maxwell-Wagner interfacial polarization. The Ti ⁴⁺ -Mn ²⁺ co-doping induced tunable structural distortions and cation redistribution, enhancing electrical resistivity while retaining magnetic functionality. These modifications, coupled with low dielectric losses at high frequencies, suggest the optimized compositions x = 0.15–0.20 are promising for high-frequency applications, such as miniaturized inductors, antennas, and electromagnetic interference shielding materials.