Synthesis and analysis of equimolar multi transition element doped spinel ferrites

A series of multi-cation substituted cobalt ferrites- CoFe₂O₄, Co₀.₅Ni₀.₅Fe₂O₄, Co₀.₃₃Ni₀.₃₃Cu₀.₃₄Fe₂O₄, Co₀.₂₅Ni₀.₂₅Cu₀.₂₅Zn₀.₂₅Fe₂O₄, and the high-entropy composition Co₀.₂Ni₀.₂Cu₀.₂Zn₀.₂Mn₀.₂Fe₂O₄ were synthesized by using solid state reaction method to investigate the effects of progressive cation substitution on the structural, optical, vibrational, and magnetic properties with increasing cation complexity. XRD and Rietveld refinement confirmed the formation of single-phase cubic spinel ferrites, with lattice expansion, peak broadening, and increased micro strain that correlate with higher cationic complexity. Configurational entropy increased systematically from 0 to 1.609 R across the series, with CNCZMFO satisfying the high-entropy criterion. SEM/EDS analysis verified uniform grain morphology and accurate elemental incorporation. FTIR and Raman spectroscopy revealed modifications in metal-oxygen vibrational modes and enhanced phonon disorder in multi-component compositions. UV–DRS analysis revealed tunable optical band gaps ranging from 1.83 to 2.25 eV, influenced by lattice distortion and cation redistribution between A- and B- sites. Magnetic hysteresis measurements demonstrated a clear transition from hard- to soft-magnetic behaviour, with coercivity decreasing significantly across the series while saturation magnetization exhibited non-monotonic variation due to cation redistribution and modified superexchange interactions. The results demonstrate that controlled incorporation of multiple transition-metal ions enables systematic tuning of lattice disorder, optical response, and magnetic softness, highlighting the potential of high-entropy spinel ferrites for applications in magnetic devices, sensors, and energy-related technologies.