Structural, optical, and magnetic properties of Co-doped ZnO nanocrystalline thin films for spintronic devices

Different compositions of Zn_1−xCo_xO (0 ≤ x ≤ 0.15) nanocrystalline compounds were produced in terms of ball milling method, thin films of these compounds were prepared by electron beam evaporation method. XRD pattern was utilized to study the structural properties of these films. Hexagonal wurtzite-type structure was displayed for all of the films. Using XRD pattern, the crystallite and lattice strain were calculated. The crystallite size decreases but the lattice strain's value rises up with accumulating dopants of Co. Increasing in lattice strain may be related to the increase in the concentration of lattice imperfections. The optical constants, n and k of the Zn_1−xCo_xO nanocrystalline films were calculated in terms of spectroscopic ellipsometry measurements in a range of 300–1100 nm. With more doping of Co, the refractive index showed an increase, as well. According to Tauc relation, the optical energy gap of the Zn_1−xCo_xO films was calculated and proved to be direct transition. The energy gap found to be decreased with the increasing of the Co concentration. In addition, studying the magnetic properties of Zn_1−xCo_xO films reveal room temperature ferromagnetism.