Optical conductivity of LSMO films on Al2O3 substrates

Abstract

AbstractWe report on the influence of temperature conditions of deposition and annealing given on the optical conductivity spectra of LSMO films. The investigated films were deposited using DC magnetron sputtering of La0.7Sr0.3MnO3 target in argon‐oxygen atmosphere on hot (T = 970 K), and cold (T=300 K) single crystalline substrates of Al2O3 (012). All films were obtained using these technologies are oxygen deficient. Optical transmission was measured in a range 1‐5 eV. The optical conductivity spectra of films with thickness more than 100 nm deposited on hot substrates are slightly dependent on the annealing. These spectra are similar to the corresponding ones of epitaxial films La0.7Sr0.3MnO3 but the typical spectral peaks are slightly shifted to higher energies.The optical conductivity spectra of unannealed films with the thickness less 100 nm which are deposited on the cold and hot substrates do not have the corresponding peak near 1 eV. We explain this fact by means of size effects and oxygen deficit. These factors suppress the mechanism of eg‐eg transition between Mn3+‐Mn4+ ions within parallel spin manifold. The three‐hour annealing in the air on the temperature interval 1070‐1170 K eliminates the oxygen deficiency in films. As a result all optical properties of all investigated films are unified. Besides, the conductivity spectra of the annealed films are similar to the corresponding ones of La0.7Sr0.3MnO3 epitaxial films. But some shift of the low‐energy peak to higher energies can be observed. It may correspond to polycrystallinity of obtained structures. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)