Tailoring the microstructure, optical, and magnetic characteristics of Co_0.6Zn_0.4Fe₂O₄ nanoferrites through Ni²⁺-Al³⁺...

Herein, Ni²⁺-Al³⁺ co-doped Co_0.6-xZn_0.4-xNi_xAl_xFe₂O₄ (0 ≤ x ≤ 0.08) nanoferrites were synthesized via a co-precipitation route to elucidate the role of defect engineering and cation redistribution in tuning optical magneto-structural properties. X-ray diffraction (XRD) confirmed single-phase cubic spinel formation with slight lattice expansion (8.3667-8.374 Å) accompanied by crystallite size reduction (16.27-11.33 nm). HRTEM and SAED analyses revealed spherical/cubic nanoparticles with high crystallinity and lattice coherence, consistent with XRD results. The increase in microstrain and dislocation density indicates enhanced lattice distortion induced by substitution. XPS analysis revealed mixed Fe²⁺/Fe³⁺ states distributed over tetrahedral and octahedral sites, enabling quantitative cation distribution modeling. The pronounced enhancement of the Raman A_1g mode confirms progressive tetrahedral distortion and cation rearrangement. The nanoferrites exhibit soft magnetic behavior with high saturation magnetization (51-58 emu/g) and low coercivity (20-79 Oe). The law of approach to saturation (LAS) analysis reveals a marked decrease in the anisotropy constant, primarily attributed to the dilution of octahedral Co²⁺ ions, reinforced by Al³⁺-induced A-B exchange weakening and nanoscale spin canting. These findings demonstrate that controlled multi-cation substitution provides an effective strategy for tailoring magnetic softness and anisotropy, making the materials promising for spintronics, high-frequency electronics, magnetic sensing, and electromagnetic interference shielding applications.