Regensburg 2010 – wissenschaftliches Programm

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KR: Fachverband Kristallographie

KR 10: Poster: Multiferroics (with MA, DF, KR, DS)

KR 10.20: Poster

Dienstag, 23. März 2010, 10:45–13:45, Poster A

Spin-phonon coupling in multiferroic stoichiometric and mixed RMnO₃ compounds (R=Gd, Tb, Eu:Y) studied by Raman spectroscopy — •S. Issing¹, A. Pimenov¹, Y. Vu. Ivanov², A. A. Mukhin², and J. Geurts¹ — ¹Physikalisches Institut, Universität Würzburg, Germany — ²General Physics Institute of the Russian Academy of Sciences, Moscow, Russia

Spin-phonon coupling, manifesting itself as phonon softening in the temperature range of the magnetically ordered phases is investigated by temperature dependent polarized Raman spectroscopy. Stoichiometric (R = Eu, Gd, Tb) and mixed (R = Eu_1−xY_x, 0≤x≤0.5 - covering the R ion radius range of the stoichiometric compounds) multiferroic orthorhombic RMnO₃ are compared in the 10 - 300 K temperature range. The strength and temperature dependence of the phonon softening depend strongly on the mody symmetry showing the correlation of this effect with the magnetic interaction of the Mn³⁺ ions within the MnO₂-plane leading to the strongest phonon renormalization for the in-plane symmetric stretching mode (B_2g(1)). Quantitative spin-phonon coupling constants for all investigated systems are derived showing the trend of weakend spin-phonon coupling for decreasing R ion radius. Strikingly, spin-phonon coupling is observed even for RMnO₃ compounds with an incommensurate magnetic structure of the Mn³⁺ spins, i.e. without long-scale magnetization. This underscores the role of phonons as a quasi-local probe.