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Vendredi 28 septembre à 13h30
Salle de conférence du bâtiment A
Orateur : Marta Elzo (MCMF)
"Studies of Multiferroic Nanostructures by Resonant X-ray Scattering"


The aim of this thesis is to explore the capabilities offered by resonant X-ray scattering for the study of multiferroic systems as ultra thin films with a special emphasis on the feasibility of such experiments under applied electric field/current. To improve the analysis capabilities, boundary propagation matrices formalism has been developed for the simulation of resonant reflectivity, using a set of eigenwaves as a basis for the computation, and has been applied to interfacial magnetic and electronic reconstruction profiles. Resonant X-ray experiments were performed on three transition metal oxides. This technique combines chemical selectivity and reciprocal space information, and was used on very thin films of PbTiO3 to solve the atomic structure of a periodic pattern of ferroelectric domains. The spectroscopic signatures observed in our hard X-ray experiments are well reproduced with FDMNES ab initio simulations. In the soft X-ray range, we studied the cycloidal antiferromagnetic structure of multiferroic BiFeO3 and especially the imprint of the cycloid on a 10 nm-thin layer of Co deposited on top of the multiferroic bulk material. We also present an experiment in which we explored the effect of an electrical current applied on a thin film of charge-ordered Pr1-xCaxMnO3. Last part is dedicated to instrumentation. We summarize the state of the art of european synchrotron beamlines and diffractometers which can host resonant X-ray diffraction experiments. Finally, we detail a new sample holder that we developed and tested in the high-vacuum diffractometer RESOXS, which allows for the application of an electric field/current.

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