  We observe a power-dependent anticrossing of Walker spin-wave modes under
microwave pumping when a ferrimagnet is placed in a microwave waveguide that
does not support any discrete photon mode. We interpret this unexpected
anticrossing as the generation of a pump-induced magnon mode that couples
strongly to the Walker modes of the ferrimagnet. This anticrossing inherits an
excellent tunability from the pump, which allows us to control the anticrossing
via the pump power, frequency, and waveform. Further, we realize a remarkable
functionality of this anticrossing, namely, a microwave frequency comb, in
terms of the nonlinear interaction that mixes the pump and probe frequencies.
Such a frequency comb originates from the magnetic dynamics and thereby does
not suffer from the charge noise. The unveiled hybrid magnonics driven away
from its equilibrium enriches the utilization of anticrossing for coherent
information processing.
