Investigation of Spin Pumping in YIG/Cu/Py using Ferromagnetic Resonance

Spin pumping in YIG/Au/Fe structures has been demonstrated where the YIG film serves as a spin battery, while the Fe film functions as a spin sink [1]. In principle, the insulating YIG film can also absorb spin currents through interfacial \emph{s-d} interactions and function as a spin sink for spin pumping. In this presentation we report on the coupling between the YIG and Permalloy (Py) films in YIG/Cu/Py systems from the viewpoint of the spin pumping effect, where both layers function as either a spin battery or a spin sink. We found an increased Gilbert damping for both the YIG and Py films by means of ferromagnetic resonance (FMR) measurements. We discuss the Gilbert damping constant ($\alpha$) of YIG(40nm), Cu(5nm)/Py(3nm), and YIG(40nm)/Cu(5, 20nm)/Py(3nm) and apply these values to spin diffusion model for the calculation of spin mixing conductance. These results show the spin pumping effect at both the ferrimagnetic/NM and ferromagnetic/NM interfaces in YIG/Cu/Py structures and the dual function of the YIG and Py films in terms of the generation and absorption of spin currents.\newline [1] B. Heinrich et. al., Phys. Rev. Lett. $\bf{107}$, 066604 (2011).