Longitudinal magnetic excitations in classical spin systems

Using spin dynamics simulations we predict the splitting of the longitudina l spin-wave peak in all antiferromagnets with single site anisotropy into t wo peaks separated by twice the energy gap at the Brillouin zone center. Th is phenomenon has yet to be observed experimentally but can be easily inves tigated through neutron scattering experiments on MnF2 and FeF2. We have al so determined that for all classical Heisenberg models the longitudinal pro pagative excitations are entirely multiple spin wave in nature.