Determination of the role of O vacancy in Co:ZnO magnetic film

Abstract

Annealing-induced changes in structural and magnetic property of Zn0.98Co0.02O thin film prepared at a low oxygen pressure by pulsed laser deposition have been studied with x-ray absorption fine structure, x-ray diffraction, and magnetization measurement. Intrinsic ferromagnetism at room temperature is observed for the as-deposited thin film, in which the Co ions are found to be substitutional for the Zn sites. Upon annealing in air, the occupation sites of Co ions keeps unchanged, whereas the magnetic property undergoes a dramatic change. X-ray absorption near-edge spectroscopy analysis and multiple-scattering calculations reveal that the change in magnetic property caused by annealing in air is due to the annihilation of the preformed oxygen vacancy. This study provides further evidence that O vacancy indeed plays an important role in activating the ferromagnetic interactions in Co-doped ZnO.