Investigating the interplay between spin polarization and magnetic damping in Co_xFe_80−xB₂₀ for magnonics applications

For magnonics and spintronics applications, the spin polarization (P) of a transport current and the magnetic damping ( α ) 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 α 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 α are measured using current-induced Doppler shifts using propagating spin wave spectroscopy and broadband ferromagnetic resonance techniques in blanket films and current-carrying Co_xFe_80−xB₂₀ alloy microstrips. The measured P ranges from 0.18 ± 0.05 to 0.39 ± 0.05, and α ranges from ( 4.0 ± 0.2 ) · 10₋₃ to ( 9.7 ± 0.6 ) · 10₋₃. We find that for increasing P, a systematic drop in α is observed, indicating an interplay between magnetic damping and the spin polarization of the transport current, which suggests that interband scattering dominates in Co_xFe_80−xB₂₀. Our results may guide future experiments, theory, and applications in advancing spintronics and metal magnonics.