Fe-doped rutile SnO2 and TiO2: local structure vs. hyperfine interactions

A. MUDARRA; C. RODRIGUEZ TORRES; F. CABRERA; M. WEISSMANN; L. ERRICO

Medellin

Congreso; XII Latin American Conference on Mossbauer Effect; 2012

Universidad de Antioquia, comite internacional LACAME

During the last years the study of transition-metal-doped TiO2 and SnO2 semiconductors has become a topic of interest, not only because of the many current industrial applications of these materials but also because of their potential use in spintronic devices. Fe-doped TiO2 and SnO2 are also of significant interest in magnetism. However, contradictory experimental as well as theoretical results were obtained, and it is uncertain whether the ferromagnetic signal (FM) found in some cases is intrinsic or comes from extrinsic magnetic phases. Conjectures were usually based on macroscopic experimental results but relatively little attention was given to the local structure around the dopants. Among other techniques, Mössbauer Spectroscopy was largely applied to study these systems. However, contradictory results were obtained, and several questions remain open concerning the location of the Fe dopants in the host structure, and/or the short range orders around impurities, as well as the assignment of the observed hyperfine interactions.             We present here an ab initio study (using the full-potential augmented plane wave plus local orbital, APW+LO method) of Fe-doped rutile SnO2 and TiO2. We performed calculations of hyperfine parameters at Fe impurities in SnO2 and TiO2 as a function of the Fe-dopant and oxygen vacancies concentrations and distributions in the hosts and assuming substitutional and interstitial site localizations for Fe in the structures. The magnetic allignment and the role of the different variables on it is discussed and  compared with available experimental data.