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Evaluation of Raman Scattering in La1-xMxMnO3 Single Crystals Due to Structural and Magnetic Transitions

Published online by Cambridge University Press:  10 February 2011

V. B. Podobedovm
Affiliation:
Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
A. Weber
Affiliation:
Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
D. B. Romero
Affiliation:
Department of Physics, University of Maryland, College Park, MD 20742, USA
J. P. Rice
Affiliation:
Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
H. D. Drew
Affiliation:
Department of Physics, University of Maryland, College Park, MD 20742, USA
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Abstract

The study of doped and undoped La1-xMxMnO3 single crystals (x = 0 to x = 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 the 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 present in distorted lanthanum manganese compounds their Raman spectra were found to contain comparable contributions from first- and 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 the 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 characterization of La1-xMxMnO3 compounds, including the inhomogeneity of the surface.

Type
Research Article
Copyright
Copyright © Materials Research Society 1998

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References

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