  Coupling between conduction electrons and localized magnetization is
responsible for a variety of phenomena in spintronic devices. This coupling
enables to generate spin currents from dynamical magnetization. Due to the
nonlinearity of magnetization dynamics, the spin-current emission through the
dynamical spin-exchange coupling offers a route for nonlinear generation of
spin currents. Here, we demonstrate spin-current emission governed by nonlinear
magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current
emission from the magnetic insulator is probed by the inverse spin Hall effect,
which demonstrates nontrivial temperature and excitation power dependences of
the voltage generation. The experimental results reveal that nonlinear
magnetization dynamics and enhanced spin-current emission due to magnon
scatterings are triggered by decreasing temperature. This result illustrates
the crucial role of the nonlinear magnon interactions in the spin-current
emission driven by dynamical magnetization, or nonequilibrium magnons, from
magnetic insulators.
