Effects of Mn₃O₄ precipitates on the vibrational properties of epitaxial Ca-doped LaMnO₃ films

This work presents a systematic study by Raman spectroscopy of the vibrational properties of La_0.7Ca_0.3MnO₃ (LCMO70/30) thin films epitaxially grown on LaAlO₃ single crystalline substrates. The epitaxial LCMO70/30 thin films were prepared using a metal organic deposition process with thermal annealing at 800 °C, 900 °C and 1000 °C, with thicknesses ranging from 20–80 nm. The evolution of the Raman modes versus film thickness and annealing temperature have been investigated. The Raman spectra of the obtained films are found to be mainly dominated by three Raman lines at 225, 440 and 661 cm⁻¹. The first two Raman lines are assigned to the vibrational modes of the LCMO70/30 films. However, by combining magnetization, x-ray diffraction and transmission electron microscopy with Raman spectroscopy, we concluded that the 661 cm⁻¹ Raman line is due to the existence of a precipitate of a Mn₃O₄ phase in the LCMO70/30 films. (paper)