Long-Range Magnetic Interactions in the Multiferroic Antiferromagnet $\rm MnWO_4$

TL;DR

This study investigates the magnetic excitations in multiferroic MnWO4, revealing complex long-range interactions and frustration that underpin its unique magnetic and magnetoelectric properties, with implications for external field control.

Contribution

The paper provides a detailed characterization of spin-wave excitations in MnWO4 and models these with a Heisenberg approach including long-range interactions, highlighting the role of frustration in its magnetic structure.

Findings

Spin-wave excitations are well described by a Heisenberg model with long-range interactions.

Magnetic frustration occurs within zigzag chains and between chains, influencing the magnetic phases.

External electric or magnetic fields can tune the magnetic interactions and phase behavior.

Abstract

The spin-wave excitations of the multiferroic $\rm MnWO_4$ have been measured in its low-temperature collinear commensurate phase using high-resolution inelastic neutron scattering. These excitations can be well described by a Heisenberg model with competing long-range exchange interactions and a single-ion anisotropy term. The magnetic interactions are strongly frustrated within the zigzag spin chain along c axis and between chains along the a axis, while the coupling between spin along the b axis is much weaker. The balance of these interactions results in the noncollinear incommensurate spin structure associated with the magnetoelectric effect, and the perturbation of the magnetic interactions leads to the observed rich phase diagrams of the chemically-doped materials. This delicate balance can also be tuned by the application of external electric or magnetic fields to achieve magnetoelectric control of this type of materials.