Magnon dispersion in MnWO4

The four magnon branches in the antiferromagnetic ground state of MnWO4 were measured by inelastic neutron scattering for two directions. On the basis of a model including isotropic Heisenberg exchange and uniaxial anisotropy, analytical expressions were derived for the dispersion relations in the spin-wave approximation using the Holstein-Primakoff and Bogoliubov transformations. By comparison between observed and calculated excitation energies, a very reliable determination of model parameters was possible. In the framework of this model, the spin deviations at absolute zero and the propagation vector slightly below the transition temperature are calculated.