Strain effect on electronic transport and ferromagnetic transition temperature in La0.9Sr0.1MnO3 thin films

We report on a systematic study of strain effects on the transport properties and the ferromagnetic transition temperature T-c of high-quality La0.9Sr0.1MnO3 thin films epitaxially grown on (100) SrTiO3 substrates. Both the magnetization and the resistivity are critically dependent on the film thickness. T-c is enhanced with decreasing the film thickness due to the compressive stain produced by lattice mismatch. The resistivity above 165 K of the films with various thicknesses is consistent with small polaronic hopping conductivity. The polaronic formation energy E-P is reduced with the decrease of film thickness. We found that the strain dependence of T-c mainly results from the strain-induced electron-phonon coupling. The strain effect on E-P is in good agreement with the theoretical predictions