Effect of angular-distortion-induced strain on structural and transport properties of epitaxial La_0.7Sr_0.3MnO₃ thin films

The effect of lattice-mismatch and especially the angle-mismatch induced strain on structural and transport properties of epitaxial La_0.7Sr_0.3MnO₃(LSMO) thin films with thicknesses of 5–70 nm has been studied by x-ray diffraction and resistivity measurements. X-ray reciprocal space maps show that the growth of LSMO films on SrTiO₃(0 0 1) and (LaAlO₃)_0.3(Sr₂AlTaO₆)_0.7(0 0 1) substrates induces biaxial tensile and compressive strain in the in-plane of the films, respectively. As the film thickness, t, is changed, there exist two distinct thickness ranges where different thickness dependence of transport properties was observed, irrespective of the strain type. For t < 12 nm, the metal–insulator transition temperature T_P is extremely sensitive to the biaxial strain and thickness, and for t ⩾ 12 nm, T_P is weakly dependent on the film thickness. We explain this variation of thickness dependence by considering the angular-distortion- induced strain and relaxation of the equilibrium rhombohedral LSMO structure.