Influence of structure characteristics on room temperature ferromagnetism of Ni-doped ZnO thin films

Abstract

The influence of structure characteristics on the ferromagnetism of Ni-doped ZnO (ZnO:Ni) thin films prepared by pulsed laser deposition has been investigated by magnetization and resistivity measurements. Structural and optical absorption analyses revealed that Ni has been incorporated into ZnO lattice as Ni2+ substituting for Zn2+ ions and the microstructure of the films becomes more inhomogeneous with increasing Ni content. The room temperature ferromagnetic (FM) behavior only occurs when Ni content is not high and the saturation magnetic moment per Ni atom decreases with increasing Ni content. No FM signal was detected for the film with 7at.% Ni content. Interestingly, the carrier density decreases with the increase of Ni doping from 1to5at.%, whereas an increase of carrier density is observed for 7at.% doped film, which indicates that carrier density alone cannot account for the FM property in ZnO:Ni films. All the results demonstrated that the microstructure of ZnO:Ni films gets more deteriorated with increasing Ni content and it is unfavorable for the long-range FM order in the ZnO:Ni films.