EFFECTS OF OXYGEN CONTENT ON THE TRANSPORT PROPERTIES OF La0.7Ca0.3MnO3-δ THIN FILMS

We report the effects of oxygen content on the transport properties of La0.7Ca0.3MnO3-δ thin films grown epitaxially on LaAlO3 (001) substrates by RF magnetron sputtering. The as-deposited thin films were annealed and treated by oxygen plasma to improve the oxygen content. We observe that the La0.7Ca0.3MnO3-δ films annealed at 850°C is highly oriented growth on (001) LAO substrate. However, the XRD patterns of the samples annealed at lower than 850°C show no distinct diffraction peaks. This evidence indicates that the samples annealed at lower than 850°C are still amorphous or nanocrystalline. The La0.7Ca0.3MnO3-δ films without oxygen plasma do not suffer insulator to metal transition at the temperature range from 213 to 293 K. But, at the same temperature range, for the 650°C, 750°C, and 850°C annealed samples with oxygen plasma treatment show an insulator to metal transition at 239 K, 239 K, and 257 K, respectively. Moreover, compared to without oxygen plasma treatment, the resistivity of the sample with oxygen plasma treatment is dramatically decreased. These results imply that the insulator to metal transition is strongly determined by the ratio of Mn4+/Mn3+ and the oxygen content of the films. The increases of the ratio of Mn4+/Mn3+ and the oxygen content lead to a higher insulator to metal transition temperature.