Direct observation of nonlinear four-magnon scattering in spin-wave microconduits

We demonstrate the intrinsic nonlinear dynamics of spin waves due to four-magnon scattering processes in a micrometer sized permalloy stripe. Spin waves are excited by a microwave current transmitted through a coplanar waveguide and the spin-wave spectrum is locally probed by Brillouin light scattering microscopy for a wide range of excitation powers. We find a transition from a purely monochromatic excitation of spin waves at low microwave powers to a large broadening of the spectrum above a certain threshold power. The spectral distributions of the measured spin waves show a unique profile, which is in excellent agreement with theoretical expectations for four-magnon scattering processes.