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Theses

Etudes structurales et magnétiques de manganites
BixCa1-xMnO3 présentant des mises en ordre complexes.

Abstract : Charge ordering phenomena and magnetism in BixCa1-xMnO3 manganites.
The structural and magnetic study was carried out on a Bi-rich part of the BixCa1-xMnO3 system, 0.7 " x " 0.5, working on ceramics and single crystals. We combine the results of different diffraction techniques – X Rays, electrons and neutrons- leaning on the transmission electron microscopy observations and correlating our results with the magnetic property. The compound x = 0,5 differs others composed by the evolution of its modulation vector as a function of the temperature. A "unique" model of the charge localization is presented for x = 0,55, 0,6 and 0,64. The charge localization is done, not on a Mn site, but on a Mn-O-Mn entity. The evolution of the magnetic structure with
Bi/Ca ratio study was performed on powder diffraction data. The data can be refined with different physicals models, in particular the classical CE-type model is one of the solutions for BixCa1-xMnO3 manganites with x=0.5. The moments tend to establish a ferromagnetic coupling with increasing x. The composite Bi0.67Ca0.33MnO3 appears as a key point for which the majority of the charge localization is destabilized. The study of the BT magnetic state of this compound confirmed the coexistence of a spin glass state and of a long range magnetic order. The origin of the spin glass state in Bi0.67Ca0.33MnO3 is interpreted as a dilution of FM domains in an AFM matrix induced by the random occupation by Bi/Ca of the A site. A similar magnetic state is shown for the Bi0.71Ca0.24MnO3 compounds when it present a type surstructure [111]p (close to the multiferroic BiMnO3 surstructure). A frustration model was proposed while basing itself on the refined orbital ordering.
Indexation Rameau: Manganite, Pérovskite, Structure cristalline (solides), Structure magnétique,
Neutrons**diffraction, Rayons X**diffraction, Microscopie électronique en transmission, Verres de spin.
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Submitted on : Monday, February 4, 2008 - 11:33:55 AM
Last modification on : Monday, February 10, 2020 - 6:12:13 PM
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  • HAL Id : tel-00235883, version 1

Citation

Maud Giot. Etudes structurales et magnétiques de manganites
BixCa1-xMnO3 présentant des mises en ordre complexes.. Matière Condensée [cond-mat]. Université de Caen, 2006. Français. ⟨tel-00235883⟩

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