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 showed that the doped Co ions were located at the Zn substitutional sites for both Zn1−xCoxO (x ≤ 0.05) and CoyZn1−yO (y ≤ 0.05) samples, magnetic measurements showed 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 revealed that the incorporation of the Zn interstitials in the lattice was crucial to the appearance of high temperature ferromagnetism in CoyZn1−yO (y ≤ 0.05) samples.

The Role of Zn Interstitials in Cobalt-Doped ZnO Diluted Magnetic Semiconductors. T.Shi, Z.Xiao, Z.Yin, X.Li, Y.Wang, H.He, J.Wang, W.Yan, S.Wei: Applied Physics Letters, 2010, 96[21], 211905