Tailoring the Optical and Magnetic Properties of Single Layered Nickel Oxide Nanocoating: A New Green Synthesis Approach

The quest for sustainable nanofabrication places green synthesis at the forefront of materials innovation. This work presents a novel, cactus plant extract-based route for depositing uniform nickel oxide (NiO) nanocoating on copper substrate via spin coating. Morphological characterization using scanning electron microscope (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) confirmed that bio-organic agents highlight the formation of spherical nanoparticles with an average grain size of 35 nm and their elemental composition respectively. X-ray diffraction (XRD) analysis revealed the formation of face-centered cubic (fcc) crystalline phase of NiO, with average crystallites 13.5 nm and 18 nm calculated using Scherrer’s equation and Williamson-Hall(W–H) plot respectively. The W–H approach separated peak broadening contributions from size and strain, yielding a more accurate estimate of true crystallite size. Rietveld refinement was employed to achieve precise diffraction parameters. Dielectric measurements showed that the dielectric constant ( $$\:{\epsilon\:}_{r}$$ ) and loss tangent ( $$\:\text{tan}\delta\:$$ ) decreases sharply at low frequencies and tends to flat at high frequency. Optical analysis indicated a narrowed band gap of 3.31 eV, while magnetic studies revealed a transition from weak ferromagnetism with exchange bias at 50 K to superparamagnetic at 300 K, driven by thermal fluctuations. These results establish a direct link between eco-friendly synthesis and tunable functional properties, positioning biosynthesized NiO as a promising candidate for next-generation optoelectronic and spintronic applications.