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Characterization of the physical, structural and electronic properties of potential multiferroics. The particular case of LuFe2O4

Vendredi 18 octobre 2013 10:30 - Duree : 1 heure
Lieu : Room 500 - 501, Central Building, ESRF - 6 Rue Jules Horowitz - Grenoble

Orateur : Sara LAFUERZA BIELSA (ICMA, Universidad de Zaragoza, Spain)

Multiferroic oxides that bring together ferroelectric and ferromagnetic orderings with added strong magnetoelectric coupling have drawn enormous attention in the last decades owing to the promising technological applications. Combined studies of their macroscopic and microscopic behaviour offer the possibility to gain new insights into the underlying mechanisms giving rise to the peculiar multiferroic properties by correlating both of them.

In this work, results on both physical properties measurements and structural and electronic characterization by means of various synchrotron radiation techniques will be presented for two different types of potential multiferroic oxides. The most significant results obtained for the Pb2MnW1-xRexO6 system will be briefly described, illustrating the extreme difficulty in preparing new multiferroics. The main part of the work is devoted to the mixed-valence system LuFe2O4, prototype of electronic multiferroic whose ferroelectricity was postulated to originate from charge ordering (CO) of Fe2+ and Fe3+. Surprisingly, the careful study of the intrinsic electrical properties has allowed us elucidating the lack of ferroelectricity in this compound. On the other hand, both high resolution powder x-ray diffraction and resonant x-ray scattering agree with a non-polar structure with a quatrimodal Fe valence distribution rather than bimodal Fe2+/Fe3+. X-ray absorption measurements confirm the maximum charge disproportionation of 0.3 e-, discarding the presence of pure ionic Fe2+ and Fe3+ and evidencing that the local structure of the Fe atom in LuFe2O4 is highly unstable. This local structure instability is consistent with a dynamical distribution of distorted bi-pyramids in the high-temperature symmetric hexagonal phase that become ordered upon cooling down, showing the order-disorder character of the so-called CO transition. Finally, some preliminary results of x-ray magnetic circular dichroism on LuFe2O4 will be also discussed within this new framework for the CO transition.

Contact : claudine.romero@esrf.fr

Discipline évènement : (Physique)
Entité organisatrice : (ESRF)
Nature évènement : (Séminaire)
Evènement répétitif : (Séminaire ESRF)
Site de l'évènement : Polygone scientifique

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