Growth of epitaxial and polycrystalline thin films of the electron doped system La_1-xCe_xMnO₃ through pulsed laser deposition

Abstract

The polycrystalline La_1-xCe_xMnO₃ manganites do not exist in single phase in bulk under the preparation conditions so far employed, but their polycrystalline and epitaxial films deposited by the pulsed laser deposition (PLD) technique form readily in single phase. The cerium oxide (CeO₂) remains partially unreacted when the bulk sample is prepared through the solid state reaction route. The resistivity of the bulk La_0.7Ce_0.3MnO₃ sample shows a broad metal insulator transition (MIT) clearly resolved into two peaks, suggesting the presence of a second (impurity) phase, which is identified as unreacted CeO₂ by the intensity analysis of the x-ray diffraction (XRD) data. However, when prepared as thin films by PLD, La_0.7Ce_0.3MnO₃ forms in single phase, as corroborated by the uniqueness and sharpness of the MIT peak and also by the XRD patterns of the polycrystalline films. We also performed a detailed study of the epitaxial films by a high-resolution XRD system with a four-circle goniometer and did not find any impurity phase. The magnetization data shows a very sharp transition followed by a sharp MIT in resistivity at the same temperature in the epitaxial thin film. These results suggest that PLD can be used as a useful technique to synthesize unconventional compounds, which do not form easily in bulk.