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Structure cristalline et magnétique de perovskites RBaMn2O6-d (où d=0 et 0.5)

Abstract : In our study we have synthesised and studied the structural and magnetic properties of the perovskite RBaMn2O6-d (where d=0 and 0.5).
Concerning the compound YBaMn2O6, DSC measurements show that it undergoes three transitions: two around 500K and a third one at 750K. X-ray and neutron diffraction studies have shown that the high temperature phase crystallises in the space group P4/nbm. The X-ray and neutron diffraction patterns show only one structural transition whereas two endothermic peaks are observed in the DSC measurements around 500K. The intermediate phase structure was refined in the space group C2/m. The charge ordered phase (that below 500K) being characterised by a low symmetry, we have realised a combined X-ray/neutron diffraction refinement. The results which were obtained show a difference of only 15%, with respect to the ideal charge separation Mn3+/Mn4+. The refinement of the magnetic structure, and the magnetic susceptibility measurements indicate the formation of Zener polarons containing four manganese cations.
The compound YBaMn2O5.5 crystallises in the space group Icma, its cell being twice that of the lanthanum same compound. This is due to the existence, in the YBaMn2O5.5 compound, of a rotation of the octahedra around the [001] direction. The refinement of the magnetic structure and the magnetic susceptibility measurements have shown that the magnetic moments of the Mn3+ cations present in the structure, are antiferromagnetically coupled.
The study of the RBaMn2O6 compounds has allowed us to establish a phase diagram as a function of rare earth cations and temperature.
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Submitted on : Wednesday, April 18, 2007 - 12:58:54 AM
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Cristian Perca. Structure cristalline et magnétique de perovskites RBaMn2O6-d (où d=0 et 0.5). Matériaux. Université Paris Sud - Paris XI, 2005. Français. ⟨tel-00076575v2⟩

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