The effect of annealing temperature on the structural, optical, and magnetic properties of ZnO@ NiFe₂O₄ nanocomposites

In the current study, ZnO/NiFe₂O₄ nanocomposites were synthesized using co-precipitation and sono-mechanical methods, followed by annealing at temperatures of 200, 500, 800, and 1100 °C. We examined their structural, optical, and magnetic properties through XRD, TEM, UV-visible spectroscopy, and VSM. XRD analysis indicates that ZnO and NiFe₂O₄ exhibit hexagonal and cubic phases, respectively. Higher annealing temperatures led to increased ferrite peak intensity and larger crystallite sizes. The optical band gap (Eg) decreased, while saturation magnetization (Ms) increased with temperature; conversely, remanent magnetization (Mr) and coercivity (Hc) decreased. Observed color changes and optical/magnetic data suggested ion exchange between ZnO and NiFe₂O₄, resulting in Zn_1−xNixO and Ni_1−xZn_xFe₂O₄ formation. All findings demonstrated that an annealing temperature of 1100 °C significantly influenced the structural, optical, and magnetic properties. Optimizing the annealing temperature is essential for modifying the physical and optical properties of Zn/5% NFO nanocomposites for various applications.