Correlation between crystal structure and magnetic behaviour in Zn-substituted Mg–Co ferrite nanoparticles

Nanocrystalline Mg0.2ZnxCo(0.8-x)Fe2O4 (x = 0.2, 0.4, 0.6, and 0.8) spinel ferrites were successfully synthesised via sol–gel auto-combustion route to investigate the influence of Zn2+ substitution on structural, morphological, magnetic, and optical properties. X-ray diffraction and Rietveld refinement confirmed the formation of a single-phase cubic spinel structure.Williamson–Hall analysis indicated nanocrystalline size and microstrain contributions. FESEM micrographs revealed nearly spherical nanoparticles. Raman and FTIR analyses corroborated the preservation of the spinel framework and indicated compositional-dependent modifications in metal–oxygen bonding. Magnetic measurements demonstrated soft ferrimagnetic behaviour at 300 K and enhanced anisotropy at 5K. Field-cooled/zero-field-cooled magnetisation and inverse susceptibility analyses revealed pronounced thermomagnetic irreversibility, and short-range ferrimagnetic correlations . UV–Visible spectroscopy showed a composition-dependent band gap variation (~1.8–2.16 eV) . The results establish a clear correlation between cation redistribution, lattice modification, and magnetic–optical response, demonstrating that Zn substitution provides an effective strategy for tailoring multifunctional properties of ferrite nanoparticles.