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A variety of semiconducting materials, called diluted magnetic semiconductors (DMS), combine two properties: semi-conductivity and magnetism. While most of the DMS havea Curie temperatue (TC) much lower than room temperature, room-temperature ferromagnetism has been observed in some Mn-doped compounds such as ZnO [1]. In 2001-2002, Co-dopedTiO2 thin films with the anatase and the rutile structures were reported to be ferromagnetic even above 400 K. These results have motivated intensive experimental [2-4] and theoretical[5] studies on the structural and electronic properties of these materials. In recent years, the theoretical and experimental studies were extended to other magnetic (Mn, Fe, Ni)and non magnetic impurities, for example, Cu [6]. However, due to intrinsic complexities, many questions remain concerning the underlying microscopic mechanism of short, middle, and long-range magnetic order and the precise location of the impurities in the host lattice. Another important question to respond is why does the doping with non magnetic elementsresult in strong ferromagnetic samples. In order to understand these questions, Cu-doped TiO2 thin films, grown by pulsed laser deposition (PLD), were studied by x-ray absorptionspectroscopy (XAFS) in order to determine the valence state and local environment of the impurities as a function of composition and to relate these features with the magneticproperties.[1] P. Sharma et al., Nature Materials 24, 673 (2003).[2] W. K. Park et al., J. Appl. Phys. 91, 8093 (2002). [3] S. A. Chambers et al., Appl. Phys. Lett. 79, 3467 (2001). [4] Y. L. Soo et al., Appl. Phys. Lett. 81, 655 (2002). [5] See, for example, L. A. Errico, M. Weissmann, and M. Rentería, Phys. Rev. B 72, 184425 (2005) and references therein. [6] S. Duhalde et al., Phys. Rev. B 72, 161313(R) (2005).

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