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Structure, dimensionnalité et magnétisme de nouvelles halogéno-cobaltites

Abstract : Among the wide diversity of hexagonal perovskite-related materials, cobalt-based systems have been widely studied because of their complex electronic and magnetic properties. The investigation of systems Ba-Co-O-X with X=F, Cl or Br has led to the synthesis of new phases with structures characterized by Co3O12 trimers (three face-shared CoO6 octahedra) or Co4O15 tetramers (four face-shared CoO6 octahedra) entities. Strong structural relationships have been pointed out between trimers and tetramers forms for oxides, oxyfluorides, oxychlorides and oxybromides compounds, with for example oxygen disorders or high temperature phases transformations (tetramers -> trimers). In these materials, the interface layer between elementary blocks is of particular importance for the dimensionality of the structures. Magnetic susceptibility measurements combined to neutrons diffraction experiments have established a paramagnetic -> antiferromagnetic transition along the c-axis in the low temperature range for halogeno-cobaltites materials. Isothermal magnetic field dependences of the magnetization have shown a more complex magnetic behaviour for the bromed materials with the possibility to align the magnetic moments in the (ab) plane by application of a magnetic field. Finally, this work deals with the relations between crystal structure, dimensionality and magnetic properties of these new halogeno-cobaltites phases.
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https://tel.archives-ouvertes.fr/tel-00198765
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Submitted on : Tuesday, December 18, 2007 - 3:53:25 PM
Last modification on : Wednesday, February 17, 2021 - 9:56:05 AM

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Matthieu Kauffmann. Structure, dimensionnalité et magnétisme de nouvelles halogéno-cobaltites. Matériaux. Université des Sciences et Technologie de Lille - Lille I, 2007. Français. ⟨tel-00198765v2⟩

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