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Etude des propriétés magnétiques et du couplage spin/réseau dans les composés multiferroïques RMnO3 hexagonaux par diffusion de neutrons.

Abstract : This manuscript is devoted to the study of magnetic properties and spin/lattice coupling in the hexagonal RMnO$_3$ compounds which belong to the multiferroic family. Most of the results were obtained from neutron scattering experiments both on powder and single crystal samples. The neutron powder diffraction data allowed us to highlight the strong coupling between atomic position and the magnetic structure stabilized. These results are discussed in terms of magnetic frustration, and we propose a model based on interplane exchange frustration. The atomic position of Mn ions relatively to a $x=1/3$ threshold is crucial in this framework. Our inelastic neutron scattering data confirmed our model by giving us access to the numerical values of some parameters from spinwave dispersions and confirmed the important role of RMn interaction on the spin dynamic. Finally, complex inelastic neutron scattering of polarized neutrons experiments showed an hybridation of spin and lattice excitations. This hybridation is interpreted within the Dzyaloshiinski-Moriya framework and numerical calculations are presented to reproduce our experimental data. This hybridation is closely related to the electromagnon observed in several multiferroic systems and seems to be inherently associated to multiferroicity.
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https://tel.archives-ouvertes.fr/tel-00551271
Contributor : Xavier Fabreges Connect in order to contact the contributor
Submitted on : Monday, March 14, 2011 - 4:39:18 PM
Last modification on : Monday, December 13, 2021 - 9:14:06 AM
Long-term archiving on: : Wednesday, June 15, 2011 - 3:06:30 AM

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Xavier Fabrèges. Etude des propriétés magnétiques et du couplage spin/réseau dans les composés multiferroïques RMnO3 hexagonaux par diffusion de neutrons.. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2010. Français. ⟨tel-00551271v4⟩

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