Observation of spin-wave Doppler shift in Co₉₀Fe₁₀/Ru micro-strips for evaluating spin polarization

The current-induced spin-wave Doppler shift has been investigated for Co₉₀Fe₁₀ films, with and without under- and overlayers of Ru, aiming to obtain quantitative insights into the value of spin polarization of the diffusive electrical currents flowing in this material. This extends the use of spin-wave Doppler shift spectroscopy beyond the study of permalloy to other soft magnetic materials suitable for use in spintronic applications such as racetrack memories. The Damon-Eshbach spin-wave mode was employed, and a control experiment of permalloy yielded a value of spin polarization of P = 0.44 ± 0.03 for that material. An extended method to properly evaluate spin-wave Doppler shifts is developed that takes account of the non-negligible Oersted fields that are generated by the current density asymmetry caused by conducting under- or overlayers. The values of spin polarization for various Co₉₀Fe₁₀-based structures are found to lie in the range of 0.3–0.35, only slightly less than in permalloy.