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

TL;DR

This study explores how spin polarization and magnetic damping are interconnected in CoFeB alloys, revealing that higher spin polarization correlates with lower damping, which is crucial for advancing magnonics and spintronics technologies.

Contribution

The paper provides experimental measurements of spin polarization and damping in CoFeB alloys and uncovers a systematic relationship between them, highlighting the role of interband scattering.

Findings

Higher spin polarization correlates with lower magnetic damping.

Interband scattering dominates in CoFeB alloys.

Results inform future spintronics and 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 $Co_{\rm x}Fe_{\rm {80-x}}B_{\rm 20}$ alloy microstrips. The measured $P$ ranges from 0.18 $\pm$ 0.05 to 0.39 $\pm$ 0.05 and $\alpha$ ranges from $(4.0\pm 0.2)\cdot10^{-3}$ to $(9.7\pm 0.6)\cdot10^{-3}$. 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 $Co_{\rm x}Fe_{\rm {80-x}}B_{\rm 20}$. Our results may guide future experiments, theory, and applications in advancing spintronics and metal magnonics.