We report on a systematic study of strain effects on the transport properties and the ferromagnetic transition temperature $T_{ c}$ of high-quality La$_{ 0.9}$Sr$_{ 0.1}$MnO$_{ 3}$ thin films epitaxially grown on (100) SrTiO$_{ 3}$ 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.
Categories: cond-mat.mtrl-sci cond-mat.dis-nn cond-mat.str-el