Tunable Structural, Optical, and Magnetic Properties of Co-Doped ZnO Thin Films for Spintronic Applications

Undoped and cobalt-doped ZnO thin films were prepared on glass substrates using the sol–gel dip-coating method, followed by annealing at 450°C. The cobalt concentration was varied between 2 and 10 at% in steps of 2 at%. X-ray diffraction analysis confirmed the formation of a hexagonal wurtzite structure, with the preferred orientation changing from (100) in the undoped films to (002) in the doped samples. UV–Visible spectroscopy indicated that the films were highly transparent (over 89%), and the optical band gap decreased from 3.327 eV to 3.211 eV as the cobalt content increased. Photoluminescence studies showed near-band-edge, blue, and green emissions, with both the absorption edge and near-band-edge emission shifting to longer wavelengths after doping. Magnetic characterization revealed that while undoped ZnO was diamagnetic, the cobalt-doped films exhibited ferromagnetic behavior at room temperature.