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Séminaire Magnétisme non conventionnel

Jeudi 17 Mars à 14h00,
Salle Remy Lemaire, K223

J. Alberto RODRIGUEZ-VELAMAZAN (ICMA, CSIC Univ Zaragoza & ILL, Grenoble)
"Magneto-electric coupling mechanisms in (NH4)2[FeCl5•H2O] multiferroic hybrid compound"

Abstract

In magnetoelectric multiferroic materials, a subtle competition between different magnetic interactions is at the origin of multiferroicity, as this competition is the responsible of the formation of a magnetic structure able to induce ferroelectric polarization. The difficulty in controlling this interplay of interactions explains the scarce number of these materials reported. (ND4)2[FeCl5·D2O] is a rare case where improper ferroelectricity has been observed in a molecular material. We have used neutron diffraction to study its crystal and magnetic structures and hence determine the mechanism of multiferroicity in this compound [1]. From the crystal structure determinations above and below 79 K, we have observed an order-disorder phase transition, which is related with the ordering of the ammonium counterion. Below TN, at zero magnetic field, we have determined the magnetic structure, which corresponds with a cycloidal spin arrangement where the magnetic moments are contained in the ac-plane and propagate along the c-direction. All the cycloids in (ND4)2[FeCl5·D2O] compound have the same chirality and therefore the ferroelectricity can be explained via the inverse Dzyaloshinskii-Moriya mechanism. The magnetic structures under applied magnetic field will be also discussed, together with the mechanisms of magneto-electric coupling in the different regions of the phase diagram.

References

1. J. A. Rodriguez-Velamazan et al. Scientific Reports 5, 14475 (2015).

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