  Interaction between quasiparticles of a different nature, such as magnons and
phonons in a magnetic medium, leads to the mixing of their properties and the
formation of hybrid states in the areas of intersection of individual spectral
branches. We recently reported the discovery of a new phenomenon mediated by
the magnon-phonon interaction: the spontaneous bottleneck accumulation of
magneto-elastic bosons under electromagnetic pumping of pure magnons into a
ferrimagnetic yttrium iron garnet film. Here, by studying the transport
properties of the accumulated magneto-elastic bosons, we reveal that such
accumulation occurs in two frequency-distant groups of quasiparticles:
quasi-phonons and quasi-magnons. They propagate with different speeds in
different directions relative to the magnetization field. The theoretical model
we propose qualitatively describes the double accumulation effect, and the
analysis of the two-dimensional spectrum of quasiparticles in the hybridization
region allows us to determine the wavevectors and frequencies of each of the
groups.
