Study on the Magnetism of Epitaxial ZnCoO Films Deposited by Pulsed Laser Deposition

Zn1-xCoxO films were deposited on Al2O3(001) substrates at different oxygen pressures with Zn0.95Co0.05O ceramic target by using pulsed laser deposition method. With X-ray diffraction (XRD), electron probe microanalysis (EPMA) and transmittance spectra, the contents of Co, Co 2+ ions and phases in the films were quan- titatively determined. The pressure dependence of Co contents in the films was given. The correlations between room-temperature magnetism and the Co, Co 2+ ions and phases in the films are discussed quantitatively. It is found that the Co content in the film decreases with the increase of oxygen pressure during the deposition. Most of Co atoms are determined to be Co 2+ ions entered the ZnO lattice to substitute for Zn 2+ ions, but not being responsible for the magnetism of the films at room temperature. The metallic Co nano-clusters are detected by fine XRD analy- sis in the films deposited at 0.0001 Pa and 5.0 Pa, being consistent with the estimation using the room-temperature magnetism of the films. On the basis of quantitative analysis, a superparamagnetic magnetization mechanism of metallic Co nano-clusters is suggested and is compared with experimental results by quantitative calculation.