CONICET | Buscador de Institutos y Recursos Humanos

Dilute magnetic impurities in semiconductors (DMS) produce novel materials thatmay be ferromagnetic at room temperature and are therefore appealing for spintronics. Thisis a rapidly developing research area because the electron spin may play a separate role, inaddition to the usual charge degree of freedom. In 2001, Co-doped TiO2 thin films with theanatase structure were reported to be ferromagnetic even above 400 K [2]. These resultshave motivated intensive experimental and theoretical studies on the structural andelectronic properties of these materials. However, many questions remain open regardingthe underlying microscopic mechanism of long-range magnetic order. Moreover, thelocation 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) ofstructural, electronic, and magnetic properties of magnetic impurities in rutile TiO2. Wefound that magnetic moments appear for Mn, Fe, and Co, but not for Ni. We also report theunexpected observation of significant room temperature ferromagnetism in asemiconductor doped with nonmagnetic impurities, Cu-doped TiO2 thin films. This wasalso found experimentally in thin films and indicates that magnetic ions are not essential toobtain ferromagnetism and that is not due to impurity clustering.In the present work we present a new series of calculations, performed with the abinitio full-potential linearized-augmented-plane-wave method (FP-LAPW) in doped TiO2and SnO2 as a function of the dopant, its concentration and also vacancy concentration. Wefind 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.

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