Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 14: Spin Systems and Itinerant Magnets

TT 14.3: Talk

Tuesday, March 27, 2007, 14:30–14:45, H19

Magnetic excitations in multiferroic TbMnO₃ — •Daniel Senff¹, Peter Link², Klaudia Hradil³, Arno Hiess⁴, Louis Pierre Regnault⁴, Yvan Sidis⁵, Nadir Aliouane⁶, Dimitri Argyriou⁶, and Markus Braden¹ — ¹II. Physikalisches Institut, Universität zu Köln — ²Forschungsneutronenquelle FRM II, TU München — ³Institut für Physikalische Chemie, Universität Göttingen — ⁴Institut Laue-Langevin, Grenoble / France — ⁵Laboratoire Leon Brillouin, Saclay / France — ⁶Hahn-Meitner-Institut, Berlin

Ferroelectricity (FE) in TbMnO₃ is intimately coupled to a complex magnetic ordering: The existence of a spontaneous electric polarization is closely correlated with a magnetic transition into an incommensurable spin-spiral structure. The critical excitations at the FE-transition are thus no longer of phononic, as in conventional ferroelectrics, but of magnetic origin.

We present extensive neutron scattering studies on the spin-wave spectrum of TbMnO₃ in the para- as well as in the ferroelectric phase [1]. We have identified the different magnon branches of the spiral structure and discus the dispersion, the field and the temperature dependence of the modes most relevant for the FE-transition. Comparing with recent optical experiments we find an excellent agreement and strengthen the interpretation of strongly mixed magnon-phonon excitations, called electromagnons, as proposed by Pimenov et al. [2].

[1] D. Senff et al., cond-mat/0610620, submitted to PRL.

[2] A. Pimenov et al., Nature physics 2 (2005) 97.