The structural and magnetic properties of Co+ implanted ZnO films

We fabricated 400 nm thick ZnO films by RF magnetron sputtering on Si (1 0 0) substrates. The eight samples were implanted by 40 keV Co+ ions at different fluences varying from 0.25 × 1017 ions/cm2 to 2.0 × 1017 ions/cm2. The XRD technique was applied to analyze the crystal structure of virgin and implanted samples. X-ray patterns show that the virgin sample has reflection peaks that originate from the (1 0 0) and (0 0 2) crystal planes. The Co+ implantation decreased the long range crystal quality and caused the formation of Co3O4 crystallites at remarkable magnitudes in the ZnO films. The theoretical analysis of the XRD data by applying Scherrer method showed that the average crystallite size dropped from 59 nm to 25 nm for ZnO samples after implantation. The magnetic properties of films were investigated by using Vibrating Sample Magnetometry (VSM). The M-H hysteresis curves of samples were recorded at room temperature and 10 K. In order to check the temperature dependence of the magnetization, we carried out field cooled (FC) and zero field cooled (ZFC) M-T measurements in a temperature range of 10-400 K. These measurements showed that the implanted samples exhibit ferromagnetic behavior at room temperature and have TC value above 1000 K. The magnetization increased with the increasing Co fluence. However, the formation of antiferromagnetic Co3O4 decreased the magnitude of magnetization. The electric conductivity of films was measured by the Four Point Probe method. The electric conductivity depends on the concentration of Co ions.