Origin of multiferrroic behavior in RMn2O5 (R=rare-earth, Y) systems
ISIS, Rutherford Appleton Laboratory, United Kingdom
Mardi 27/03/2007, 14:30
LLB - Bât 563 p15 (Grande Salle), CEA-Saclay
Multiferroic materials have recently attracted a considerable interest, in particular with the discovery of large magnetoelectric coupling in a variety of frustrated magnetic systems such as TbMnO3, the Kagome staircase compound Ni3V2O8 or RMn2O5 (R=rare earth). All these systems are improper ferroelectic, and the onset of an electric polarization (P) is strongly coupled to the development of complex magnetic order, often incommensurate. The spin-lattice coupling mechanism can involve antisymmetric exchange term SixSj or symmetric exchange ("exchange-striction"), each of them imposing constraints in the direction of P and leading to different behavior under magnetic field. I will review recent results on these systems and discuss further the origin of ferroelecticity in RMn2O5 (R=Tb,Y), in the light of neutron diffraction results.