Investigation of annealing-induced oxygen vacancies in the Co-doped ZnO system by Co K-edge XANES spectroscopy

To clarify the mechanism of the observed room-temperature ferromagnetism (RTF), many studies have been focused on dilute magnetic semiconductor systems. Several investigations have demonstrated that oxygen vacancies play a significant role in mediating the RTF behavior so that much effort has been devoted to confirm their presence. In this investigation, X-ray absorption spectroscopy was combined with ab initio calculations of the electronic structure of Co and Zn in the Zn_0.9Co_0.1O system before and after annealing, which has been recognized as an effective method of originating oxygen vacancies. A feature at about 20 eV after the rising edge of the Co K-edge XANES that disappears after annealing has been associated with the presence of an oxygen vacancy located in the second shell surrounding the Co atom. Moreover, Zn K-edge XANES spectra point out that this oxygen vacancy affects the electronic structure near the Fermi level, in agreement with density functional theory calculations.