Role of cobalt in ZnO : Co thin films

Abstract

We prepared a series of Co-doped thin films using the pulsed laser deposition method at deposition temperatures from 400 to 800 °C under oxygen pressures from 10 −4 to 15 Pa. We found that the ferromagnetic signals in ZnO : Co thin films only appear simultaneously with the detectable Co 2p spectra from incompletely oxidized Co metal. Therefore, we concluded that the ferromagnetism in ZnO : Co thin films is not an inherent magnetism in the material. On the other hand, we proposed that the inhomogeneous distribution of Co in the films could improve the link of the grains and increase the carrier concentration of the films, leading to positive Hall signals although the film is n-type. Therefore, the coexistence of ferromagnetism and p-type conductivity in ZnO : Co thin films need to be re-examined carefully.