The study of doped and undoped La1-xMxMnO3 single crystals [x= O to 0.3] in the temperature range from 5 K to 423 K is reported. The activity of phonon vibrational modes in optical spectra is analyzed and a comparison to experimental Raman data is presented. Different contributions from optical phonons to Raman scattering process are discussed. It is shown that both the value of doping and temperature have a significant influence on Raman features and these are strongly affected by structural and magnetic phase transitions. Due to the symmetry conditions in distorted lanthanum manganese compounds their Raman spectra were found to contain comparable contributions from first- and the second-order phonon scattering. The common features related to both the reduction of the Jahn-Teller [JT] distortion and the temperature- induced phase transition were found in the Raman spectra of La1-xMxMnO3 crystals. An anomalous behavior of the low-frequency Raman mode in doped systems was found and explained in terms of temperature-dependent ionic radius of the La/Sr ion sites. It was found that the strong dependence of the Ag Raman mode on the value of doping may serve as a useful tool for optical diagnostics of La1-xmxMnO3 compounds, including the inhomogeneity of the surface.
Citation: Science and Technology of Magnetic Oxides Materials Research Society Symp Proc
Publisher Info: MRS, Pittsburgh, PA, Volume: 494, -1
Pub Type: Books
phonons, Raman scattering, structure