Evaluation of nonlinear effect in high power spin pumping in polycrystalline bi-substituted yttrium iron garnet (Bi:YIG)/Pt bilayer structure

We have demonstrated a quantitative evaluation of spin pumping at uniform excitation in linear and nonlinear regimes of microwave absorption in a polycrystalline Bi-substituted yttrium iron garnet (Bi:YIG)/Pt bilayer structure. The evaluation is performed based on a ratio of magnitude of pumped spin currents to amplitude of uniform precession which are estimated from inverse spin Hall effect voltage and microwave absorption intensity at various incident powers. The ratio shows additional contribution to spin pumping by spin waves generated from uniform precession via nonlinear coupling between them. We have also clarified the additional contribution by the generated spin waves at various frequencies based on the ratio.