Probing of a parametrically pumped magnon gas with a non-resonant packet   of traveling spin waves
  The magnon gas created by spatially localized longitudinal parametric pumping in an yttrium-iron-garnet film is probed by a traveling packet of spin waves non-resonant with the pumping field. The analysis of the influence of the magnon gas on the amplitude and phase of the propagating spin waves allows to determine characteristic properties of the parametrically pumped magnon gas. A simple theoretical model is proposed from which the magnon density in the pumping region is calculated. 
T. Neumann, A. A. Serga, B. Hillebrands