Sintering-driven structural and thermal evolution of Mn-substituted CoFe2O4 spinel ferrites

Mn-substituted CoFe2O4 nanomagnetic materials were successfully synthesized via the sol–gel auto-combustion method and sintered at 900 °C, 1000 °C, and 1100 °C. The structural, morphological, vibrational, and thermal properties were systematically investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermal analysis (TGA/DTG/DSC). XRD results confirmed the formation of a single-phase cubic spinel structure with space group Fd-3m and an average lattice parameter of approximately 8.376 Å. The crystallite size increased from ~10.32 nm to ~14.36 nm with increasing sintering temperature, indicating enhanced crystallinity. FESEM analysis revealed agglomerated nanoparticles with particle sizes ranging from ~94 to 140 nm, with improved uniformity at higher temperatures. FTIR spectra showed characteristic metal–oxygen vibrations at ~580 cm⁻¹ and ~400 cm-1, confirming spinel ferrite formation. Raman analysis exhibited typical A1g, T2g, and E g modes with a red shift of ~2–5 cm-1, indicating lattice distortion due to Mn substitution. Thermal analysis demonstrated a three-stage weight loss with total mass reduction decreasing from ~13.8% (900 °C) to ~7.1% (1100 °C), confirming improved thermal stability. DSC results revealed reduced endothermic and exothermic peak intensities with increasing sintering temperature, indicating enhanced phase formation and reduced residual content. The results demonstrate that higher sintering temperature significantly improves crystallinity, structural stability, and material homogeneity, making Mn-substituted CoFe2O4 a promising candidate for advanced magnetic and electromagnetic applications.