Investigating the Interplay between Spin-Polarization and Magnetic Damping in ${\mathrm{Co}}_x{\mathrm{Fe}}_{80-x}{\mathrm{B}}_{20}$ for Magnonics Applications

Abstract

For magnonics and spintronics applications, the spin polarization ($P$) of a transport current and the magnetic damping ($\alpha$) play a crucial role, e.g. for magnetization dynamics and magnetization switching applications. In particular, $P$ in a glassy (amorphous) 3d transition ferromagnet such as CoFeB and $\alpha$ are both strongly affected by $s-d$ scattering mechanisms. Hence, a correlation can be expected which is a priori difficult to predict. In this work, $P$ and $\alpha$ are measured using current-induced Doppler shifts using propagating spin-wave spectroscopy and broadband ferromagnetic resonance techniques in blanket films and current-carrying $C{o}_{\mathrm{x}}F{e}_{80-\mathrm{x}}{B}_{20}$ alloy microstrips. The measured $P$ ranges from 0.18 $\pm$ 0.05 to 0.39 $\pm$ 0.05 and $\alpha$ ranges from $(4.0\pm 0.2)\cdot 10^{-3}$ to $(9.7\pm 0.6)\cdot 10^{-3}$. We find that for increasing $P$ a systematic drop in $\alpha$ is observed, indicating an interplay between magnetic damping and the spin polarization of the transport current which suggests that interband scattering dominates in $C{o}_{\mathrm{x}}F{e}_{80-\mathrm{x}}{B}_{20}$. Our results may guide future experiments, theory, and applications in advancing spintronics and metal magnonics.