CONICET | Buscador de Institutos y Recursos Humanos

Dilute magnetic impurities in semiconductors (DMS) produce novel materials that may be ferromagnetic at room temperature and are therefore appealing for spintronics. This is a rapidly developing research area because the electron spin may play a separate role, in addition to the usual charge degree of freedom. In 2001, Co-doped TiO2 thin films with the anatase structure were reported to be ferromagnetic even above 400 K [2]. These results have motivated intensive experimental and theoretical studies on the structural and electronic properties of these materials. However, many questions remain open regarding the underlying microscopic mechanism of long-range magnetic order. Moreover, the location and distribution of the impurities in the host lattices is still unclear. In 2003, we started a systematic ab initio study (using DFT-based methods) of structural, electronic, and magnetic properties of magnetic impurities in rutile TiO2. We found that magnetic moments appear for Mn, Fe, and Co, but not for Ni. We also report the unexpected observation of significant room temperature ferromagnetism in a semiconductor doped with nonmagnetic impurities, Cu-doped TiO2 thin films. This was also found experimentally in thin films and indicates that magnetic ions are not essential to obtain ferromagnetism and that is not due to impurity clustering. In the present work we present a new series of calculations, performed with the ab initio full-potential linearized-augmented-plane-wave method (FP-LAPW) in doped TiO2 and SnO2 as a function of the dopant, its concentration and also vacancy concentration. We find that magnetism depends strongly on the impurity location (substitutional or interstitial) on vacancy concentration and in some cases on the impurity concentration. [1] Y. Matsumoto et al., Science 291, 854 (2001). [2] L. A. Errico, M. Weissmann and M. Rentería, Phys. Rev. B 72, 184425, 2005. [3] S. Duhalde et al., Phys. Rev. B 72, 161313(R), 2005.