Strain induced x-ray absorption linear dichroism in La0.7Sr0.3MnO3 thin films

Strain induced anisotropy in the electronic properties of La0.7Sr0.3MnO3 thin films was investigated by x-ray absorption spectroscopy at the Mn 2p and O 1s edges. Films on (100) SrTiO3 and (100) LaAlO3 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)-y(2) (3z(2)-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.