CONICET | Buscador de Institutos y Recursos Humanos

The discovery of room-temperature ferromagnetism (RTF) in Co-doped anatase [1] and rutile [2] TiO2 has stimulated intense theoretical and experimental studies of these systems due to their potential applications in spintronic technology. In effect, dilute magnetic semiconductors (DMS), produced by doping non magnetic semiconductors with transition metals, combine their electric conductivity with ferromagnetism and optical transparency, thereby opening up the possibility of new device concepts. But, the site of the impurity is still under debate and while some authors claimed that the presence of ferromagnetic metallic clusters can not be completely excluded, others have concluded that ferromagnetism is a consequence of atomic scale doping [3]. Recently, we reported the experimental observation of unexpected and significant RTF in Cu-doped TiO2 films [4], equivalent to what would be expected if, on the average, each Cu atom bears a magnetic moment of about 1.5 mB. This result indicates that the presence of impurity clustering is not necessary to obtain ferromagnetic order. A large magnetic moment was also obtained from ab initio calculations, but only if an oxygen vacancy in the nearest-neighbor shell of Cu is present [4]. In order to clarify the role of impurities in DMS on the presence of magnetism it is crucial to determine the local environment of magnetic and non magnetic impurities. In this work we present an EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Spectroscopy) characterization of the local environment of transition metal (TM)-doped anatase TiO2 thin films (TM=Co, Ni, Cu, and Zn). [1] Y. Matsumoto et al., Science 291, 854 (2001). [2] W. K. Park et al., J. Appl. Phys. 91, 8093 (2002). [3] See, e.g., H. Weng et al., Phys. Rev. B 73, 121201 (2006), and refs. therein [4] S. Duhalde et al., Phys. Rev. B 72, R161313 (2005).