title: Geometric local structure at the Mn site in charge-ordered mixed valence manganites.
abstract: An extensive study of Mn K-edge absorption sepctroscopy has been carried out in La(1-x)Ca(x)MnO3 and Tb(1-x)Ca(x)MnO3 (x=0, 0.33, 0.5, 0.67, 1) series as a function of temperature.  The EXAFS analysis for the charge ordering compounds (x > or = 0.5) shows the presence of a static distortion of the MnO6 octahedron in the whole temperature range. However, this local distortion is lower than the distortion found for Jahn-Teller compounds. Magnetoresistive compounds (x=0.33) show a regular octahedron in the low temperature metallic phase. Instead, no changes are found for the first coordination shell (Mn-O) across the charge ordering transition while Mn-Mn distribution shows minor variations with the temperature. The structural analysis of the second coordination shell suggests that the Mn-O-Mn angle is the most relevant parameter to describe the electric and magnetic behaviour of these compounds.
authors.affiliation: Instituto de Ciencia de Materiales de Arogón, C.S.I.C.-Universidad de Zaragoza, Spain. csanchez@posta.unizar.es
authors.forename: M C
authors.initials: MC
authors.lastname: Sánchez
authors.forename: J
authors.initials: J
authors.lastname: García
authors.forename: G
authors.initials: G
authors.lastname: Subías
authors.forename: J
authors.initials: J
authors.lastname: Blasco
authors.forename: M G
authors.initials: MG
authors.lastname: Proietti