Strain induced x-ray absorption linear dichroism inLa0.7Sr0.3MnO3thin films

Strain induced anisotropy in the electronic properties of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ thin films was investigated by x-ray absorption spectroscopy at the Mn $2p$ and O $1s$ edges. Films on (100) $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ and (100) $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ substrates were grown by pulsed laser deposition with in situ reflection high energy electron diffraction diagnostic. At both absorption edges, clear features related to different anisotropic lattice strain effects as a function of the substrate were observed. On the average a negative (positive) linear dichroism was obtained for films grown under in-plane tensile (compressive) epitaxial strain conditions. Indeed, the structural macroscopic distortion induced by the substrate is responsible of the octahedra distortions with the resulting stabilization of ${x}^{2}\text{\ensuremath{-}}{y}^{2}$ $(3{z}^{2}\text{\ensuremath{-}}{r}^{2})$ orbitals. Enhanced linear dichroism at the Mn $2p$ edge in very thin films, only a few unit cells thick, is in agreement with a fully strained state which favors the formation of orbital ordered phase regions.