Field dependence of magnetic correlations through the polarization flop transition in multiferroic TbMnO3 : evidence for a magnetic memory effect

The field-induced multiferroic transition in TbMnO3 has been studied by neutron scattering. Apart strong hysteresis, the magnetic transition associated with the flop of electronic polarization exhibits a memory effect: after a field sweep, TbMnO3 does not exhibit the same phase as that obtained by zero-field cooling. The strong changes in the magnetic excitations across the transition perfectly agree with a rotation of the cycloidal spiral plane indicating that the inverse Dzyaloshinski-Moriya coupling causes the giant magnetoelectric effect at the field-induced transition. The analysis of the zone-center magnetic excitations identifies the electromagnon of the multiferroic high-field phase.