Metal-insulator transition in epitaxial films of LaMnO$_3$ manganites grown by magnetron sputtering

We have studied thin films of LaMnO$_3$ manganite grown by RF magnetron sputtering at high pressure on crystalline substrates with cubic symmetry. It is established that these films exhibit a metal-insulator transition, whereas LaMnO$_3$ grown on orthorhombic substrates remains in a dielectric state. The parameters of the metal-insulator transition have been studied as dependent on the level and symmetry of mechanical stresses that arise during the epitaxial growth of LaMnO$_3$ films on various substrates. The resistance of LaMnO$_3$ films grown on SrTiO$_3$ substrates has been studied as a function of the film thickness. It is found that the presence of excess oxygen due to substitution in the cation system can significantly influence the Mn$^{4+}$/Mn$^{3+}$ ion ratio in the film and thus lead to the appearance of the metal-insulator transition.