Ferromagnetic Resonance to Investigate Spin Pumping in Permalloy Multilayers

Coplanar Waveguide Ferromagnetic Resonance Spectroscopy (CPW-FMR) was used to investigate the spin dynamics of the thin film multilayers Py/Ir vs. Py/Cu/Ir. The properties of both sample sets were evaluated as a function of the Ir thickness. The gyromagnetic ratio, , is found to be independent of the Ir thickness and determined to be approximately 29.4 GHz/T for all samples. The magnetization, M, is found to be 7249 G for the Py/Cu/Ir samples compared to 7630 G for the Py standard. For the Py/Ir bilayer, M decreases as Ir thickness increases, ranging from 7641 G to 7293 G. The thickness dependence on M for Py/Ir is believed to be caused by induced perpendicular anisotropy. The inhomogeneous broadening (ΔH0) is nearly double for Py/Ir compared to Py/Cu/Ir. There is a strong enhancement of the Gilbert damping parameter when the Ir layer has a direct interface with magnetic layer (α = 0.023) compared to when the interfaces are interrupted with a Cu layer (α = 0.013). The control sample Py demonstrated a damping parameter consistent with other investigations (α = 0.0084). This indicates the presence of spin memory loss at the interface of Py and Ir. Effective Spin mixing conductance, geff, was found to be 8.8 ± 0.3 nm−2 for Py/Cu/Ir, and 25.2 ± 0.5 nm−2 for the Py/Ir samples. There is a thickness dependence on the damping for the Py/Ir samples that was not observed Py/Cu/Ir samples. This is believed to be related to a proximity effect for the Py-Ir interface. The thickness dependence on the damping for Py/Ir was found to be approximately λ=0.5 ± 0.1 nm