Contribution of spin pumping to magnon-magnon coupling in YIG/Py heterostructure

We investigate the strong correlation between magnon-magnon coupling (M-M coupling) and coherent spin pumping in yttrium iron garnet/permalloy (Y3Fe5O12, YIG/Py) heterostructure through spin-torque ferromagnetic resonance technique. We demonstrate experimentally that the spin pumping of hybrid modes is the strongest near the coupling region at 295 K, indicating that coherent spin pumping is closely associated with magnon hybridization. Meanwhile, the coupling strength g(c) increases from 0.26 to 0.37 GHz with temperature reduction from 295 to 260 K, which is attributed to the enhancement of spin pumping, especially the hybrid mode characterized by spin pumping out of Py that provides a pronounced contribution. Furthermore, the increased linewidth of the hybrid mode near the coupling region at low temperatures leads to enhanced spin mixing conductivity. This enhancement, in turn, improves spin pumping. Our experiments discuss the underlying mechanisms that influence coupling strength in detail, providing deeper insights into tuning M-M coupling.