Tuning the structural, optical and magnetic properties of transition metal doped zinc oxide nanoparticles

Transition metal Ni²⁺ doped ZnO nanoparticles were prepared by surfactant-aided co-precipitation route with the general formula Zn_1-xNi_xO (x = 0.00, 0.04, 0.08, and 0.12). The influence of transition metal doping on the structural, optical, and magnetic characteristics of ZnO nanoparticles has been explored employing a variety of characterization techniques, such as x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) for structural characterization, ultra violet visible spectroscopy (UV–Vis), photoluminescence spectroscopy (PL) for optical characterization, and vibrating sample magnetometer (VSM) for magnetic characterization. All the samples had a single-phase hexagonal structure with a mean crystallite size ranging from 22 to 26 nm. HRTEM was used to study the size distribution and morphology of the particles. The optical energy band gap was initially found to blue shift from 3.27 to 3.36 eV when Ni dopant level increased from 0 to 8%, and further red shifted from 3.36 to 3.29 eV when the Ni dopant level increased from 8 to 12%. The PL study shows a broad violet emission band at 425 nm, indicating the presence of zinc interstitials and oxygen interstitial defects in the ZnO lattice. Room temperature magnetization (M–H) loops suggested that the diamagnetic behaviour of ZnO changes to weak ferromagnetism when doped with Ni. A saturation magnetization of 0.18 emu/g was seen for the ZnO sample doped with 8% Ni²⁺. Since achieving room temperature ferromagnetism is crucial for dilute magnetic semiconductors, our study presents a valuable contribution for spintronics and high-frequency applications.