Evidence Of Phonon Pumping By Magnonic Spin Currents

Spin current phenomena are at the heart of the active research field of spintronics that aims to develop new perspectives for emerging information technologies. In recent years, several groups reported experiments in which spin currents are used to excite coherent magnetization dynamics in magnetic nanostructures. Here, we show experimentally two effects of the large spin current generated by the giant spin Hall effect in a platinum strip with nanoscopic silver particles adjacent to a film of the insulating ferrimagnet yttrium iron garnet (YIG). The first, demonstrated by ferromagnetic resonance (FMR) experiments, is the dramatic reduction of the magnon damping measured by the FMR linewidth due to the spin torque produced by the spin current. The second, observed by Brillouin light scattering (BLS), is the excitation of quasi-particles in the YIG film with frequencies that do not vary with the applied magnetic field. We interpret the BLS signal as due to phonons excited by the magnonic spin current injected into the YIG film, in a process that is the Onsager reciprocal of the spin pumping by coherent elastic waves.