On specific properties of easy plane antiferromagnets

In antiferromagnets (AF) with an easy plane (EP) type of anisotropy (and in easy axis AF with flopped sublattices) dynamic effects are possible with the participation of "quasiantiferromagnetic" magnons. These effects have no analogs in ferrites. It is especially interesting to realize the possibility of parametric excitation of phonons not coupled linearily with magnons.