Determination of spin pumping as a source of linewidth in sputtered Co${}_{90}$Fe${}_{10}$/Pd multilayers by use of broadband ferromagnetic resonance spectroscopy

Determination of spin pumping as a source of linewidth in sputtered Co $_{90}$ Fe $_{10}$ /Pd multilayers by use of broadband ferromagnetic resonance spectroscopy

Justin M. Shaw, Hans T. Nembach, and T. J. Silva

Phys. Rev. B 85, 054412 – Published 10 February 2012

Abstract

We performed a systematic study of damping in Co $_{90}$ Fe $_{10}$ /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 $Δ$ $H_{0}$ . Samples were prepared with net perpendicular anisotropy field values ranging from −0.5 to $+$ 1.2 T. $Δ$ $H_{0}$ shows a dependence on the perpendicular anisotropy, though the Landau-Lifshitz damping parameter $α$ , which ranged from 0.016 to 0.04, exhibits no trend as a function of anisotropy. We explain the wide variation of $α$ as a result of spin pumping from Co $_{90}$ Fe $_{10}$ into adjacent nonmagnetic layers. We use a quantitative model for spin pumping that includes the intrinsic spin-mixing conductance at the Co $_{90}$ Fe $_{10}$ /Pd interface and the spin-diffusion length of Pd, which were experimentally measured at room temperature to be (1.07 $\pm$ 0.13) $\times$ 10 $^{19}$ m $^{- 2}$ and 8.6 $\pm$ 1.0 nm, respectively. We quantitatively show how $α$ is enhanced by spin pumping through an FMR investigation of individual Pd/CoFe/Pd, and Pd/CoFe/Pd/CoFe/Pd layer structures.