Evaluation of spin waves and ferromagnetic resonance contribution to the spin pumping in a Ta/CoFeB structure

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 3 μm, magnetostatic surface spin waves with a large wavevector (k) of about 0.81 μm^-1 are excited. A large k value results in the 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 wave contribution is about 1 at large bias fields in a 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 ± 1.27 μm in the Ta/CoFeB structure at a bias field of 600 Oe.