Sol-gel auto-combustion synthesis of CoFe2O4 spinel nanoparticles with ferrimagnetic and semiconducting properties

Abstract

Cobalt ferrite (CoFe₂O₄) is a multifunctional spinel oxide whose structural, optical, and magnetic properties are strongly influenced by the synthesis route and thermal treatment. Establishing the relationship between the synthesis conditions and the resulting structural, compositional, optical, and magnetic characteristics is essential for assessing the properties of the material obtained by sol-gel auto-combustion. Here, we synthesized CoFe₂O₄ powder by a urea-assisted sol-gel auto-combustion route and systematically characterized it to determine its crystal structure, chemical composition, optical response, and magnetic behavior. The precursors were dissolved in distilled water and heated progressively to 420 °C to promote spontaneous combustion; the resulting powder was subsequently calcined at 700 °C for 3 h. X-ray diffraction followed by Rietveld refinement confirmed the formation of a single-phase cubic inverse-spinel structure with space group Fd-3m and a lattice parameter of 8.3801 Å. SEM observations revealed fine, predominantly irregular to sub-spherical particles with moderate agglomeration; particle dimensions were estimated to be on the order of 100 nm, while EDS analysis showed a composition close to the nominal CoFe₂O₄ stoichiometry. Diffuse-reflectance measurements and Kubelka–Munk analysis yielded a direct optical band gap of 1.45 ± 0.05 eV. Room-temperature magnetization measurements up to 15 kOe revealed ferrimagnetic behavior, with a magnetization approaching 50 emu g⁻¹ at the maximum applied field. These results establish the structural, compositional, optical, and magnetic characteristics of CoFe₂O₄ produced by the selected sol-gel auto-combustion route and provide a basis for further studies of its functional properties.