Evaluation of Spin Waves and Ferromagnetic Resonance Contribution to the Spin Pumping in Ta/CoFeB Structure

TL;DR

This study investigates how spin waves and ferromagnetic resonance contribute to spin pumping in Ta/CoFeB structures, revealing the dominant FMR contribution at high bias fields and proposing a method to measure spin wave decay.

Contribution

It provides a quantitative analysis of spin wave and FMR contributions to spin pumping and introduces a new method to characterize spin wave decay in Ta/CoFeB interfaces.

Findings

FMR contribution exceeds spin waves at high bias fields.

Spin wave decay length is approximately 5.5 μm at 600 Oe.

Method to quantify spin wave decay constant is proposed.

Abstract

The spin waves and ferromagnetic resonance (FMR) contribution to the spin pumping signal is studied in the Ta/CoFeB interface under different excitation bias fields. Ferromagnetic resonance is excited utilizing a coplanar waveguide and a microwave generator. Using a narrow waveguide of about 3 {\mu}m, magnetostatic surface spin waves with large wavevector (k) of about 0.81 {\mu}m^-1 are excited. A large k value results in dissociation of spin waves and FMR frequencies according to the surface spin wave dispersion relation. Spin waves and FMR contribution to the spin pumping are calculated based on the area under the Lorentzian curve fitting over experimental results. It is found that the FMR over spin waves contribution is about 1 at large bias fields in Ta/CoFeB structure. Based on our spin pumping results, we propose a method to characterize the spin wave decay constant which is found to be about 5.5 {\mu}m in the Ta/CoFeB structure at a bias field of 600 Oe.