Oxygen diffusion in different thicknesses La$_{0.8}$Sr$_{0.2}$MnO$_{3-\delta}$ films on NdGaO$_{3}$ substrates

The results of investigation by the indirect method of step-by-step varying the oxygen content in the series of epitaxial La$_{0.8}$Sr$_{0.2}$MnO$_{3-\delta}$ films on single-crystal NdGaO$_{3}$ substrates are presented. Using numerical simulation we have revealed that the oxygen diffusion coefficient significantly decreases along the film thickness in the direction from the outer surface to the film-substrate interface under conditions of “compressive” mechanical stresses caused by the mismatch of the in-plane crystalline parameters of the film and substrate materials. In films of $d\approx$ 12 – 75 nm thickness, the effect is manifested in the fact that the value of the diffusion coefficient in the vicinity of the outer surface of the films also decreases significantly as the thickness of the films decreases. The questions of the applicability of the indirect method for evaluating the oxygen content in thin epitaxial films, as well as other manifestations of effects caused by mechanical stresses are discussed.