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

TL;DR

This study investigates how the local atomic structure of REOFeAs oxypnictides varies with different rare-earth elements using Fe K-edge EXAFS, revealing insights into bonds relevant for superconductivity and magnetism.

Contribution

It provides systematic analysis of inter-atomic distances and MSRD in REOFeAs, highlighting the covalent Fe-As bond and the effects of chemical pressure on other bonds.

Findings

Fe-As bond length remains nearly unchanged, indicating covalent bonding.

Fe-Fe and Fe-RE bond lengths decrease with smaller rare-earth ions.

Results suggest atomic correlations influence superconductivity and magnetism.

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.