Role of oxygen content in thickness dependent phase transition temperatures in La0.9Sr0.1MnO3 films

Abstract

Thickness dependent phase transition temperatures of manganite epitaxial films are generally attributed to the variation in epitaxial strain, but the role of oxygen content is rarely considered and analyzed quantitatively. Herein, low-doped La0.9Sr0.1MnO3 (LSMO) films with thickness range (tf) of 15–175 nm were prepared and post-annealed in air, the thickness dependent oxygen content and transport properties were studied. The metal-insulator transition (MIT) appears in LSMO films (tf = 20–175 nm), accompanied by a dramatic enhancement in Curie temperature (TC). Furthermore, the phase transition temperatures TMI and TC show an unexpected drop after reaching the maximum in LSMO film (tf = 70 nm). This phase transition temperatures variation could not be explained by the decrease of compressive strain with the increasing thickness, the variation of oxygen content should be considered. Analysis on Mn3+/Mn4+ ratio shows the excess of oxygen induced by post-annealing leads to the lower Mn3+/Mn4+ ratio approaching to the optimal value and stronger double exchange (DE) interaction, and DE interaction reaches the strongest in LSMO film (tf = 70 nm) because of the optimal Mn3+/Mn4+ ratio. Our study reveals that oxygen content plays a primary role in the thickness dependent phase transition temperatures by modulating Mn3+-Mn4+ double exchange interaction.