Local structure and magnetism of Cu-doped ZnO via Cu K-edge XAS and XMCD: Theory and experiment

We investigate theoretically the sensitivity of Cu K-edge XANES and XMCD of Cu-doped ZnO (Cu:ZnO) to the local structure. We find that the sensitivity is high enough to enable to distinguish between geometries conceivable for Cu:ZnO. However, one cannot distinguish between Cu and Zn in further coordination shells. Likewise, presence of oxygen vacancies in the ab plane does not alter XANES or x-ray linear dichroism (XLD). By analysing experimental XANES and EXAFS signals of Cu:ZnO pellets (which are paramagnetic) and Cu:ZnO films (which are ferromagnetic) we find that for the pellets, Cu is in Zn-substitutional sites while for the films, the coordination of Cu is as in CuO. Cu K-edge XMCD measurements were performed for both types of samples but detectable signal was obtained only for the pellets. The theory confirms that this XMCD signal originates from magnetic moments localised at Cu atoms located in Zn-substitutional sites.