Epitaxial strain induced metal insulator transition in La0.9Sr0.1MnO3 and La0.88Sr0.1MnO3 thin films

We are reporting an unexpected metal insulator transition at the ferromagnetic phase-transition temperature for thin films of ${\mathrm{La}}_{\mathrm{0.9}}{\mathrm{Sr}}_{\mathrm{0.1}}{\mathrm{MnO}}_{\mathrm{3}}$ (<50 nm), grown on a (100) face of ${\mathrm{SrTiO}}_{\mathrm{3}}$ substrate. For the thicker films (>50 nm), similar to the single crystal, no such transition is observed below $T_C.$ Additionally, we observe the suppression of the features associated with charge or orbital ordering in intentionally La-deficient thin films of ${\mathrm{La}}_{\mathrm{0.88}}{\mathrm{Sr}}_{\mathrm{0.1}}{\mathrm{MnO}}_{\mathrm{3}}$ (<75 nm). In thin films, transmission electron microscopy reveals a compressive strain due to the epitaxial growth, that is, lattice parameters adopt those of the cubic lattice of ${\mathrm{SrTiO}}_{\mathrm{3}}.$ As the film thickness increases, coherent microtwinning is observed in the films and the films relax to a orthorhombic structure.