Regensburg 2016 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 11: Poster
DF 11.16: Poster
Mittwoch, 9. März 2016, 18:00–20:00, Poster E
Impact of temperature-dependent local and global ordering in RMnO3 for electromagnons and spin-phonon coupling. — •Sebastian Elsässer1, Markus Schiebl2, Alexey Shuvaev2, Alexander Mukhin3, Jean Geurts1, and Andrei Pimenov2 — 1Universität Würzburg, Exp.Physik 3, Würzburg, Germany — 2Institut für Festkörperphysik, TU Wien, Wien, Austria — 3General Physics Institute of the Russian Academy of Sciences, Moscow, Russia
The perovskite-like rare-earth manganites RMnO3 are among the most widely studied compounds in multiferroics. The inverse Dzyaloshinskii - Moriya (DM) interaction with cycloidal spin ordering is generally accepted as the driving mechanism of magnetically induced ferroelectricity in compounds with e.g. R=Dy3+, Tb3+, (Eux:Y1−x)3+, (Eux:Ho1−x)3+. This DM coupling leads to the emergence of electromagnons (EM), i.e. electro-active spin waves that can be excited by a.c. electric fields. The magnetic order also induces shifts of specific phonon frequencies due to spin-phonon coupling (SPC). After usual view, the EM should only occur for the ferroelectric state with cycloidal magnetic order at T<TFE≈ 25K, and the SPC below TN≈45K. However, we observe the EM and SPC already far above TN. The occurrence of the EM for T>TFE can be explained in terms of cycloids with opposite chirality and T-dependent correlation lengths, which simulate a sinusoidal magnetization pattern for TFE<T<TN, and a disorder-order transition at TFE. Along the same line, the gradual occurrence of SPC already far above TN can be understood in terms of an onset of locally spin-ordered areas already in this T-range.