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College Park, Maryland      June 6 - 10 , 2004

T3-A1 (3:45 PM): Charge, orbital and spin ordering in RBaFe2O5+x perovskites (Invited)

P. M. Woodward (Department of Chemistry, Ohio State University), P. Karen (Department of Chemistry, University of Oslo)

Transition-metal oxides adopting the perovskite structure (or closely related structure types) are well known for their interesting electronic properties (i.e. High TC superconductivity, colossal magnetoresistance, charge disproportionation, etc.). The oxygen-deficient double perovskites RBaFe2O5+x (R = Nd, Sm, Tb, Ho, Y) are among the more interesting classes of perovskite related compounds. When x = 0 these compounds contain square-pyramidal iron with an average valence of +2.5. By changing temperature all three Robin-Day classes of iron mixed-valence can be observed. In the high temperature paramagnetic state all iron atoms are equivalent. Upon cooling antiferromagnetism sets in, followed by a two-step charge-localization process. The localization of the conduction electrons triggers phenomena such as charge and orbital ordering, reorientation of the antiferromagnetic structure and in some cases induced magnetism of the rare-earth sublattice. Variable temperature high-resolution synchrotron x-ray and neutron powder diffraction measurements, neutron thermodiffractometry, transport and magnetic susceptibility measurements are used to characterize the behavior of this interesting family of compounds.

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