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. Shi, T., Xiao, Z., Yin, Z., Li, X., Wang, Y., He, H., Wang, J., Yan, W., Wei, S.: Applied Physics Letters, 2010, 96[21], 211905