This work reports an O K-edge X-ray
absorption spectroscopy (XAS)
study of Al-doped ZnO nanoparticles and films showing room-temperature
ferromagnetism (RTFM). The origin of this ferromagnetism remains controversial
as different conclusions are derived for analogous systems. Among
those, charge-transfer effects and the presence of vacancies are often
suggested, based on the modification of similar XAS spectra with respect
to that of undoped ZnO. We present here a critical re-examination
of the reported O K-edge absorption in these materials, by comparing
the experimental spectra to ab initio theoretical
calculations, paying special attention to the role of structural modifications,
instead of the currently accepted electronic interpretation, into
driving the observed spectral modifications. Our results indicate that the reported variations of the XAS spectral
profile are not due to the charge-transfer effects involving Al and
O, but are associated with the structural modification of the oxygen
next-neighboring arrangement. Indeed, the structural changes are in
agreement with the formation of interfaces between ZnO and alumina-based
regions, upon the reaction between ZnO and Al. According to previous
studies, the RTFM likely resides in these interfaces associated with
the oxygen ions.