Spin Waves and Magnetic Interaction in the Multiferroic Antiferromagnet MnWO4

The spin wave excitations of the multiferroic MnWO4 have been measured in the low-temperature collinear commensurate phase using high-resolution inelastic scattering. The spin excitations can be well described by a Heisenberg model with competing exchange interactions up to 11th nearest neighbors. We find the magnetic exchange couplings are highly frustrated within each zigzag spin chain along c-axis and between chains along the a-axis. However, the magnetic interactions are much weaker between chains along the b-axis. Our measurements suggest that the delicate balance of long range magnetic couplings is subject to small perturbations that can lead to a complex magnetic configuration exhibiting magnetoelectric behavior.