The role of Zn interstitials in cobalt-doped ZnO diluted magnetic semiconductors

Co-doped ZnO samples Zn1−xCoxO and CoyZn1−yO were prepared by the sol-gel and magnetron sputtering methods, respectively. Although the Co K-edge extended x-ray absorption fine structure spectra show that the doped Co ions are located at the Zn substitutional sites for both Zn1−xCoxO (x≤0.05) and CoyZn1−yO (y≤0.05) samples, magnetic measurements show paramagnetism in Zn1−xCoxO (x≤0.05) and high temperature ferromagnetism in CoyZn1−yO (y≤0.05). An experimental and numerical study of the O K-edge x-ray absorption near-edge structure spectra reveals that the incorporation of the Zn interstitials in the lattice is crucial to the appearance of high temperature ferromagnetism in CoyZn1−yO (y≤0.05) samples.