Magnetism and heterogeneity of Co in anatase Co:TiO_2 magnetic semiconductor

摘要

Using x-ray magnetic circular dichroism (XMCD), x-ray absorption spectroscopy (XAS), and energy filtered transmission electron microscopy, we provide evidence for a heterogeneous Co distribution in anatase Co:TiO_2 magnetic semiconductor having a low Co concentration (1.4 at. %). Multiplet structure due to Co~(2+) is observed in XAS spectra, but suppressed due to the coexistence of metallic Co clusters and substitutional Co ions, whereas XMCD spectra resemble metallic Co. The presence of Co~(2+) can be correlated with earlier observations of impurity band conduction and Kondo behavior, whereas metallic Co clusters contribute to the ferromagnetism and anomalous Hall effect.