Metal–insulator transition temperature dependence on lead and oxygen content in La1−xPbxMnO3±y thin films

Abstract

Preparation of the manganese oxide films with high Curie temperature (TC) above room temperature (RT) is essential for developing multilayered devices that work at RT. We have fabricated La1−xPbxMnO3±y (LPMO) thin films on LaAlO3–Sr2AlTaO6 (001) single-crystal substrates using a pulsed-laser ablation deposition method. Their metal–insulator transition temperature (TRmax), which nearly equals TC, is investigated as a function of the lead (Pb) and oxygen contents contained. The results in the following were obtained. X-ray diffraction indicates growth of epitaxial films with (001) orientation. Samples with high TRmax∼370 K can be prepared in deposition conditions with a substrate temperature (TS) of 600 °C and an oxygen pressure (PO) not less than 0.4 Torr. The TRmax decreases with increasing TS or decreasing PO. The former decrease in the TRmax is shown by electron-probe microanalysis to be ascribed to evaporation of Pb from the films at high TS. On the other hand, it is inferred that the latter decrease is due to a reduction in oxygen content in the films. The reduction of Pb and oxygen contents in the LPMO films, respectively, leads to a decrease in the number of conduction electrons and, consequently, results in a TRmax decrease of the films.