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

Abstract The Ti⁴⁺-Mn²⁺ co-doped cobalt ferrite nanoparticles, CoFe2-2xTixMnxO₄ (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 (Ti⁴⁺, Mn²⁺) and host (Co²⁺, Fe³⁺) 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 Fe²⁺ and Fe³⁺ ions as Ti⁴⁺ and Mn²⁺ occupied octahedral sites. Dielectric parameters (permittivity, loss tangent) decreased with rising frequency 1 kHz-1 MHz, typical of Maxwell-Wagner interfacial polarization. The Ti⁴⁺-Mn²⁺ 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.