Enhancement of electrical and ferromagnetic properties by additional Al doping in Co: ZnO thin films

Several properties of Al-doped Zn0.95Co0.05O thin films prepared by radio frequency (RF) magnetron co-sputtering have been systematically investigated. The experimental results indicate that Co2+ steadily substitutes for tetrahedrally coordinated Zn2+ in the ZnO wurtzite lattice without any segregated secondary phase formation, and that a trace amount of additional Al doping has a profound influence on the enhancement of electrical and magnetic properties of Co:ZnO films. All the films show room-temperature ferromagnetism, and a giant magnetic moment of 3.36 mu(B)/Co is obtained in the Zn0.948Co0.05Al0.002O thin film. The ferromagnetic ordering is seen to be correlated with the structural defects. Moreover, a phenomenon of band gap broadening and absorption edge blueshift can be achieved by additional Al doping into the Co:ZnO films.