Substitution Effect on the Structural, Magnetic, and Electrical Properties of Co1−xZnxFe2O4 Nanocrystalline Ferrites ( $x = 0$ –1) Prepared via Gelatin Auto-Combustion Method

Co_1-xZnxFe₂O₄ ferrites (x = 0-1) were successfully synthesized, for the first time, via sol-gel auto-combustion route using gelatin fuel. The auto-combustion was characterized using DTA-TG-DSC up to ferrite formation, and an appropriate gelation mechanism was suggested. The structural, morphological, magnetic, and electrical properties were investigated through X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), ac-conductivity, and dielectric constant measurements. XRD indicated the need for further calcination at 350 °C to obtain well crystalline ferrites. The slight changes in the lattice values up to x = 0.8 suggested the substitution of Zn²⁺ ions for the Co²⁺ ions located in the octahedral sites. The large change at x = 1 suggested the conversion into the normal spinel structure. Based on the structural data, an appropriate distribution for cations was suggested. This distribution was reinforced using FT-IR and magnetic measurements. TEM showed dense agglomeration at low substitutions released by increasing Zn-content. VSM exhibited hard magnetic properties with an obvious transition from ferromagnetic to paramagnetic by increasing zinc. The maximum saturation magnetization (56.7 emu/g) was obtained for Co_0.8Zn_0.2Fe₂O₄. The behavior of magnetization with Zn-substitution was explained in the view of the cationic stoichiometry. The coercivity decreases by increasing zinc, which was attributed to the anisotropic nature of zinc. AC-conductivity versus temperature revealed a semiconducting behavior with an obvious change from ferroto paramagnetic by rising temperature. The conduction mechanism as well as the type of the charge carriers was discussed in the view of calculated activation energies and the frequency dependence of conductivity. The measured dielectric constants gave results that agreed well with the conductivity data.