Determination of spin pumping as a source of linewidth in sputtered Co90Fe10/Pd multilayers by use of broadband ferromagnetic resonance spectroscopy

We performed a systematic study of damping in Co90Fe10/Pd multilayers by use of broadband (1-60 GHz) ferromagnetic resonance (FMR) spectroscopy in the perpendicular geometry. The data were fitted with the conventional Landau-Lifshitz equation in conjunction with an inhomogeneous contribution to linewidth Delta H-0. Samples were prepared with net perpendicular anisotropy field values ranging from -0.5 to + 1.2 T. Delta H-0 shows a dependence on the perpendicular anisotropy, though the Landau-Lifshitz damping parameter alpha, which ranged from 0.016 to 0.04, exhibits no trend as a function of anisotropy. We explain the wide variation of alpha as a result of spin pumping from Co90Fe10 into adjacent nonmagnetic layers. We use a quantitative model for spin pumping that includes the intrinsic spin-mixing conductance at the Co90Fe10/Pd interface and the spin-diffusion length of Pd, which were experimentally measured at room temperature to be (1.07 +/- 0.13) x 10(19) m(-2) and 8.6 +/- 1.0 nm, respectively. We quantitatively show how alpha is enhanced by spin pumping through an FMR investigation of individual Pd/CoFe/Pd, and Pd/CoFe/Pd/CoFe/Pd layer structures.