Green synthesis of NiFe₂O₄, CoFe₂O₄, and Ni_0.5Co_0.5Fe₂O₄ by sol–gel autocombustion method using olive leaf extract as fuel

Nickel ferrite (NFO), cobalt ferrite (CFO), and nickel-cobalt (NCFO) ferrite were produced by a green synthesis method utilizing olive leaf extract as a fuel (OLE). The study aims to assess the structural and magnetic characteristics of ferrite nanoparticles produced via green synthesis with olive leaf extract. This method seeks to decrease toxicity and environmental impact while enhancing properties like size, shape, and composition to improve performance. Crystal structure, microstructure, and magnetic properties were studied using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, energy-dispersive X-ray spectroscopy, and vibrating sample magnetometry. The NFO, CFO, and NCFO ferrites display a single cubic spinel structure belonging to the Fd-3 m space group with crystallite sizes ranging from 123 to 170 nm. The lattice parameter (a) increases from 8.3499±10^-4Å for NFO to 8.3673±10^-4 Å and 8.3872±10^-4 Å for Co-containing NCFO and CFO ferrites, respectively. The estimation of the cation distribution from the Rietveld refinement reveals that the CFO shows a higher inversion degree of 0.67 compared to that of NFO and NCFO ferrites (δ = 0.46). The CFO, NFO, and NCFO samples exhibit mixed ferrite structures. Fourier-Transform Infrared spectroscopy measurements confirm the formation of the spinel structures. The saturation magnetization, coercivity, remanence, and constant anisotropy K1 of the cobalt-containing CFO and NCFO ferrites are higher than those of NFO.