Dresden 2011 – scientific programme

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KR: Fachgruppe Kristallographie

KR 5: Poster Multiferroics (Joint Session of MA, DF, DS, KR, TT)

KR 5.46: Poster

Tuesday, March 15, 2011, 10:45–13:00, P2

Coupling Effects between Lattice dynamics and Magnetism in GdMnO₃ studied by optical spectroscopy — Sven Issing¹, Michael Schmidt², Franz Mayr², Joachim Deisenhofer², Alois Loidl², Alexander A. Mukhin³, Andrei Pimenov⁴, and •Jean Geurts¹ — ¹Experimentelle Physik III, Universität Würzburg, Germany — ²Experimentelle Physik V, Universität Augsburg, Germany — ³General Physics Institute of the Russian Academy of Sciences, Moscow, Russia — ⁴Institut für Festkörperphysik, Technische Universität Wien, Austria

We present detailed optical reflectivity FT-IR investigations of the temperature dependence of the infrared active phonons in the multiferroic manganite GdMnO₃ from T = 300K down to T = 5K. GdMnO₃ is in the focus of interest due to its intimately coupled orbital, lattice and spin degrees of freedom and the resulting multiferroism. Our results clearly show two different coupling effects shifting the phonon frequencies at the onset of the magnetically ordered phases: Spin-Phonon Coupling (SPC) and Electromagnon-Phonon Coupling (EMPC). SPC is caused by a modulation of the magnetic exchange by a movement of the O²⁻ ions within the MnO₂ plane. Thus, it is most strongly pronounced for phonons consisting mainly of distortive modes of the MnO₆ octahedra within this plane. We observed a softening of the phonon frequencies by Δ ω ≈ −(1−2)%. EMPC on the other side manifests itself as a strong hardening of the phonon frequency (Δ ω ≈ + 3%) for the B_3u(1) mode, which is mainly a Gd³⁺ and Mn³⁺ displacement. It is clearly connected with the appearance of the Electromagnon.