53 research outputs found
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
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