Room temperature ferromagnetism in Co-doped ZnO films synthesized by magnetron sputtering

A systematic investigation on the microstructure, optical, and magnetic properties of Co-doped ZnO films is reported. Zn1-xCoxO films were synthesized using magnetron sputtering technique, which could produce economically feasible large area films with good crystalline properties even at a low substrate temperature. Structural analysis indicates that the wurtzite ZnO crystal can be well retained up to a Co composition of atom fraction 8%. All the samples show high transparency in the visible region. There are three absorption bands located on 567, 615, and 659 nm in the optical transmittance spectra for Co doped ZnO films, which correspond to the electronic transition of Co 3d orbitals in the oxygen tetrahedron, showing the incorporation of Co into the Zn sites in the wurtzite ZnO host lattice. The magnetic measurements indicate that all the Co doped ZnO films are ferromagnetic at room temperature and the concentration of Co doping plays an important role in the magnetic properties of Zn1-xCoxO thin films. Considering the structural, electrical, and magnetic investigations, the ferromagnetism observed in our samples should be an intrinsic property of Co doped ZnO films and can be described by bound magnetic polarons models with respect to defect-bound carriers.