Zn²⁺ Induced Structural and Functional Modulations in CoFe₂O₄ Thin Films Synthesized by Spray Pyrolysis

Abstract

Zn²⁺-substituted cobalt ferrite (Co₁₋ₓZnₓFe₂O₄, where 0.0 ≤ x ≤ 1.0) thin films were successfully fabricated using the spray pyrolysis technique. X-ray diffraction (XRD) analysis confirmed the formation of a single-phase cubic spinel structure, indicating successful ionic substitution. The lattice constant increased from 8.3443 to 8.4314 Å with increasing Zn²⁺ concentration. Field emission scanning electron microscopy (FE-SEM) revealed uniformly distributed, spherical, and agglomerated nanoparticles with grain sizes increasing from 41 nm to 78 nm. Atomic force microscopy (AFM) showed dense films with smooth surface morphology and enhanced crystallinity. Optical studies using UV–Visible spectroscopy indicated a direct allowed electronic transition, with the optical band gap narrowing from 2.75 eV to 2.41 eV due to lattice expansion and defect-induced localized states. DC resistivity measurements confirmed semiconducting behavior, showing a decrease in resistivity with increasing temperature. Magnetic characterization using vibrating sample magnetometry (VSM) revealed a gradual decrease in saturation magnetization, remanence, and coercivity with higher Zn²⁺ content. These results suggest that Zn²⁺ ions preferentially occupy the A-site, causing redistribution of Co²⁺ and Fe³⁺ ions between tetrahedral and octahedral sites, thereby modifying the magnetic exchange interactions. The optimized Co–Zn ferrite thin films exhibit potential for applications in magnetic sensors, memory devices, and optoelectronic systems.