Neutron Diffraction, Structural and Magnetic Properties of (La1-YPry)0.9Na0.1MnO3

A systematic study of the structural and magnetic properties of the diluted perovskite manganite oxides (La1-yPry)0.9Na0.1MnO3 (0.2≤y≤0.8) had been carried on. in this study, the average ionic radius 〈rA〉 of a cation site was systematically varied while keeping fixed the carrier concentration (Mn3+/Mn4+ ratio). X-Ray diffraction investigations showed a structural transition from the rhombohedral to the orthorhombic system for 0.33≤y≤0.5. the unit cell volume decreases with increasing Pr3+ content. Magnetic measurements showed that our synthesized samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. Neutron diffraction studies show that (La0.2Pr0.8)0.9Na0.1MnO3 powder sample crystallizes in the orthorhombic system with Pnma space group at room temperature and at 10 K. the magnetic moment of Pr and Mn atoms are coupled parallel to the b-axis. © 2002 Elsevier Science B.V. All rights reserved

Synthesis and structure of new pyrochlore-type oxides Ln2ScNbO7 (Ln = Pr, Nd, Eu, Gd, Dy)

We report the synthesis and structural study of mixed oxides in the Ln2ScNbO7 series. New phases with Ln = Pr, Eu, Gd and Dy are obtained. All crystallize in the cubic pyrochlore structure type, space group F-d3m, with no Sc-Nb ordering on the B-site. The structures are determined by Rietveld refinement. The evolution of cell parameters, interatomic distances and angles as a function of lanthanide cation size is discussed. Magnetic measurements show the absence of ordering down to 2 K, in agreement with the presence of strong geometric frustration in the lanthanide sublattice. The europium phase shows a peculiar magnetic behaviour; its magnetic susceptibility becomes constant below ca 50 K. This feature confirms the behaviour observed previously on Eu2Ti2O7 and is ascribed to crystal field effects

Electron spin resonance in heavily doped TMMC : Cu

We report ESR measurements in the one-dimensional Heisenberg paramagnet (CH3)4NMn1-xCuxCl3 for x ranging between 0 and 0.5. The room temperature results show a maximum of the linewidth for a concentration x ~ 0.25, in agreement with the altered diffusion model, with the notable exception of the magic angle orientation. A lineshift towards low fields is observed in strongly doped samples. At lower températures, ESR is also modified by the impurities, in accordance with the réduction of the short time effects and the enhancement of the diffusive contribution.Nous donnons les résultats de mesures de RPE dans le paramagnétique de Heisenberg unidimensionnel (CH3)4NMn1 -xCuxCl 3, x étant compris entre 0 et 0,5. A température ambiante la largeur de raie est maximum pour une concentration x ~ 0,25 en accord avec le modèle de la diffusion freinée. On note cependant une exception pour l'orientation correspondant à l'angle magique. On observe un déplacement de la raie vers les bas champs dans les échantillons les plus dopés. La RPE est aussi modifiée par les impuretés aux basses températures. Les mesures sont en accord avec une réduction de la contribution gaussienne et une augmentation de la contribution diffusive

Essai de valorisation d'écarts de triage de dattes : élaboration et caractérisation d'un extrait concentré de la pulpe.

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Voies de valorisation des pulpes de dattes.

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