Tuning Structural and Optical Properties of Co₀.₅Mn₀.₅₋ₓZnₓFe₂O₄ Nanoferrites via Zn Substitution for Optoelectronic Applications

Ferrite nanoparticles are interesting materials due to their rich and unique physical and chemical properties. They find applications in catalysis, bio-processing, medicine, magnetic recording, adsorption, devices, so nanoferrite materials had been synthesized to produce new alternate substance for reducing the rare or high cost of industrial materials. Therefore,Co_0.5Mn_0.5-xZn_xFe₂O₄ nanoferrite compositions (x=0,0.1,0.2,0.3,0.4) were successfully synthesized via the citrate-nitrate sol-gel auto-combustion technique. A comprehensive investigation of structural and optical, properties was conducted using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and UV–Vis diffuse reflectance spectroscopy (DRS). XRD analysis confirmed the formation of a single-phase cubic spinel structure with space group Fd-3m, without detectable secondary phases, indicating the successful incorporation of Zn²⁺ and Mn²⁺ ions into the cobalt ferrite lattice. The crystallite size was found to vary between 8.017 and 10.130 nm depending on Zn substitution. Rietveld refinement further verified the structural stability with a lattice parameter of a = 8.370 Å and satisfactory fit (x² = 0.15). Microstructural parameters such as dislocation density, microstrain, and stacking fault probability were found to increase with decreasing crystallite size. The FTIR spectroscopy confirmed the formation of spinel ferrite and spectra exhibited characteristic metal–oxygen vibration bands at approximately 585 cm⁻¹ and 415 cm⁻¹, corresponding to tetrahedral and octahedral sites of the spinel structure. UV–Vis DRS analysis revealed strong absorption in the UV–visible region, with the optical band gap decreasing from 2.96 to 2.81 eV as the Zn concentration increased, demonstrating tunable electronic properties. The absorption coefficient, extinction coefficient, imaginary dielectric constant, and optical conductivity increased with Zn substitution, whereas the refractive index and real dielectric constant showed an opposite trend, with a maximum refractive index observed near 2.6 eV (475 nm). The enhanced optical conductivity around 3.6 eV was attributed to interband transitions and charge-transfer processes such as O^2- → Fe³⁺ and Fe²⁺ ↔ Fe³⁺. These results demonstrate that Zn substitution effectively tailors the optical response of Co–Mn ferrites, highlighting their potential for optoelectronic and photonic applications.