Local structure of ReFeAsO (Re = La, Pr, Nd, Sm) oxypnictides studied by Fe K-edge EXAFS

¹  Dipartimento di Fisica, Università di Roma “La Sapienza" - P. le Aldo Moro 2, 00185 Roma, Italy, EU
²  Laboratoire CRISMAT, CNRS UMR 6508, ENSICAEN - Boulevard du Marechal Juin, 14050 Caen, France, EU
³  Department of Physics and Astronomy, Vrije Universiteit - De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands, EU
⁴  European Synchrotron Radiation Facility - 6 Rue Jules Horowitz, BP 220, 38043 Grenoble Cedex 9, France, EU
⁵  Department of Materials Science and Engineering, State University of New York at Stony Brook Stony Brook, NY 11794, USA
⁶  Brookhaven National Laboratory - Upton, NY 11973, USA

Corresponding author: naurang.saini@roma1.infn.it

Received: 22 June 2009
Accepted: 9 July 2009

Abstract

Local structure of ReOFeAs (Re = La, Pr, Nd, Sm) system has been studied as a function of chemical pressure varied due to different rare-earth size. Fe K-edge extended X-ray absorption fine structure (EXAFS) measurements in the fluorescence mode has permitted to compare systematically the inter-atomic distances and their mean square relative displacements (MSRD). We find that the Fe-As bond length and the corresponding MSRD hardly show any change, suggesting the strongly covalent nature of this bond, while the Fe-Fe and Fe-Re bond lengths decrease with decreasing rare-earth size. The results provide important information on the atomic correlations that could have direct implication on the superconductivity and magnetism of ReOFeAs system, with the chemical pressure being a key ingredient.