Spin waves in the one- or two-dimensional classical Heisenberg ferromagnet with a hard magnetization axis

With a suitable definition, magnons can exist in a magnetically disordered medium with any wavelength at sufficiently low temperature, but they can only be observed by neutron scattering at small wavelengths. The neutron inelastic scattering cross section is accurately calculated at low temperature in a special model for one- and two-dimensional media.