  Parallel pumping of nuclear spin waves in antiferromagnetic CsMnF3 at liquid
helium temperatures and magnetoelastic waves in antiferromagnetic FeBO3 at
liquid nitrogen temperature in a helical resonator was studied. It was found
that the absorbed microwave power is approximately equal to the irradiated
power from the sample and that the main restriction mechanism of absortption in
both cases is defined by the nonlinear radiation damping predicted about two
decades ago. We believe that the nonlinear radiation damping is a common
feature of parallel pumping technique of all normal magnetic excitations and it
can be detected by purposeful experiments.
