Local tetragonal distortion in La₀.₇Sr₀.₃MnO₃ strained thin films probed by x-ray absorption spectroscopy

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We report on an angular resolved X-ray Absorption Spectroscopy study of La₀.₇Sr₀.₃MnO₃ thin films epitaxially grown by pulsed laser deposition on slightly mismatched substrates which induce tensile or compressive strains. XANES spectra give evidence of tetragonal distortion within the MnO₆ octahedra, with opposite directions for tensile and compressive strains. Quantitative analysis has been done and a model of tetragonal distortion reflecting the strain has been established. EXAFS data collected in plane for tensile substrate confirm the change in the Mn-O average bond distance and the increase of Mn-Mn length matching with the enlargement of the cell parameter. From these results we conclude that there is no significant change in the Mn-O-Mn angle. Our observations conflict with the scenarios which this angle is the main driving parameter in the sensitivity of manganite films properties to external strains and suggest that the distortion within the octahedra plays a key role in the modification of the transport and magnetic properties.