Local tetragonal distortion in La_{0.7}Sr_{0.3}MnO_3 strained thin films probed by x-ray absorption spectroscopy

摘要

We report on an angular resolved X-ray Absorption Spectroscopy study of$La_{0.7}Sr_{0.3}MnO_{3}$ thin films epitaxially grown by pulsed laserdeposition on slightly mismatched substrates which induce tensile orcompressive strains. XANES spectra give evidence of tetragonal distortionwithin the $MnO_{6}$ octahedra, with opposite directions for tensile andcompressive strains. Quantitative analysis has been done and a model oftetragonal distortion reflecting the strain has been established. EXAFS datacollected in plane for tensile substrate confirm the change in the $Mn-O$average bond distance and the increase of $Mn-Mn$ length matching with theenlargement of the cell parameter. From these results we conclude that there isno significant change in the $Mn-O-Mn$ angle. Our observations conflict withthe scenarios which this angle is the main driving parameter in the sensitivityof manganite films properties to external strains and suggest that thedistortion within the octahedra plays a key role in the modification of thetransport and magnetic properties.