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Etude des pyrochlores géométriquement frustrés R2M2O7 (M=Sn ou Mo). Influence des substitutions chimiques et/ou de la pression appliquée

Abstract : In the oxides R2M2O7, both R3+ (rare earth or Y) and M4+ (M= sp or transition metal) form geometrically frustrated pyrochlore lattices. The object of the present study is the analyse of two types of systems: (i) Tb2Sn2O7, an insulating compound where the energy balance and the ground state are controlled by the magnetic interactions between Tb3+ ions only and (ii) (Tb1-xLax)2Mo2O7 (x=0-0.2) series, having both localized Tb3+ and partially itinerant Mo4+ ions magnetism. We have studied the magnetic order mainly by neutron diffraction and Muon Spin Rotation and Relaxation (µSR), which due to their complementarity yield a microscopic picture of both static spin correlations and spin fluctuations. Under the effect of chemical substitution and/or applied pressure we have observed a great variety of magnetic behaviours when varying temperature: short range orders (spin liquids or spin glasses), original long range order (“ordered spin ices”) or mixed phases. We have tried to understand in each case the role played by the rare earth and/or the transition metal ions in order to determine how the magnetic interactions favour a particular magnetic ground state.
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Anca Mihaela Apetrei. Etude des pyrochlores géométriquement frustrés R2M2O7 (M=Sn ou Mo). Influence des substitutions chimiques et/ou de la pression appliquée. Matière Condensée [cond-mat]. Université Paris Sud - Paris XI, 2007. Français. ⟨tel-00229792⟩

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