Raman and infrared studies of La_1-ySr_yMn_1-xM_xO_3 (M=Cr, Co, Cu, Zn, Sc or Ga): Oxygen disorder and local vibrational modes

Abstract

We present results of our study of polarized Raman scattering and infrared reflectivity of rhombohedral ceramic La_1-ySr_yMn_1-xM_xO_3 manganites in the temperature range between 77 and 320K. In our samples, a part of the Mn atoms is substituted by M = Cr, Co, Cu, Zn, Sc, or Ga with x in the range 0 -- 0.1. The hole concentration was kept at the optimal value of about 32% by tuning the Sr content y. We have monitored the distortions of the oxygen sublattice by the presence of broad bands in the Raman spectra, the increase of d.c. resistivity extracted from the infrared reflectivity, and the change of the critical temperature of the ferromagnetic transition. Our results support the idea, that these properties are mainly determined by the radius of the substituent ion, its electronic and magnetic structure playing only a minor role. Furthermore, the Raman spectra exhibit an additional A_g-like high frequency mode attributed to the local breathing vibration of oxygens surrounding the substituent ion. Its frequency and intensity strongly depend on the type of the substituent. In the Co-substituted sample, the mode anomalously softens when going from 300 to 77K. The frequency of the bulk A_{1g} mode depends linearly on the angle of the rhombohedral distortion.

11 pages, 11 Figures, best-fit values table added, a discussion added

References in corpus (5)

• Structural phenomena associated with the spin-state transition in LaCoO3
• Raman phonons as a probe of disorder, fluctuations and local structure in doped and undoped orthorhombic and rhombohedral manganites
• Determinative Role of the Jahn-Teller Disorder in the Raman Scattering of Mixed-Valence Manganites
• The interplay between double exchange, super-exchange, and Lifshitz localization in doped manganites
• The effect of Cu substitution on the A1g mode of La(0.7)Sr(0.3)MnO3 manganites

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• Spin-phonon interaction and short range order in $\mathrm{M}{\mathrm{n}}_3\mathrm{S}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_6$
• Effect of Mn substitution by Ga on the optical properties of a metallic manganite