Spin-wave dispersion and magnon chirality in multiferroic TbMnO3

TL;DR

This study uses advanced neutron scattering techniques to explore magnon behavior and chirality in multiferroic TbMnO3, revealing controllable dynamic chirality linked to static multiferroic order.

Contribution

It provides a comprehensive experimental and theoretical analysis of magnon dispersion and chirality in TbMnO3, including the effects of Tb3+ moments and external electric fields.

Findings

Magnon dispersion matches spin-wave calculations with complex interactions.

Dynamic chirality can be controlled by electric fields.

Magnon behavior becomes more complex with Tb3+ ordering.

Abstract

Inelastic neutron scattering experiments combining time-of-flight and polarized techniques yield a comprehensive picture of the magnon dispersion in multiferroic TbMnO3 including the dynamic chirality. Taking into account only Mn3+ moments, spin-wave calculations including nearest-neighbor interactions, frustrating next-nearest neighbor exchange as well as single-ion anisotropy and antisymmetric terms describe the energy dispersion and the distribution of neutron scattering intensity in the multiferroic state very well. Polarized neutron scattering reveals strong dynamic chirality of both signs that may be controlled by external electric fields in the multiferroic phase. Also above the onset of long-range multiferroic order in zero electric field, a small inelastic chiral component can be inverted by an electric field. The microscopic spin-wave calculations fully explain also the dynamic chirality of magnetic excitations, which is imprinted by the static chirality of the multiferroic phase. The ordering of Tb3+ moments at lower temperature reduces the broadening of magnons but also renders the magnon dispersion more complex.