Spin pumping and transport in the Ni80 Fe20 /Pt/Co asymmetric trilayer

Abstract

Ferromagnet1/nonmagnetic metal/ferromagnet2 (FM1/NM/FM2) trilayers have garnered considerable attention because of their potential in spintronic applications. A thorough investigation of the spin transport properties of these trilayers is therefore important. Asymmetric trilayers, particularly those including platinum (Pt) as a spacer, are less explored. Pt mediates exchange coupling between the two FM layers and thus offers a unique platform to investigate the spin transport properties under indirect exchange coupling conditions through the spin-pumping mechanism. We study the static and dynamic magnetic properties of a Ni80Fe20/Pt(t)/Co trilayer system through vibrating sample magnetometry and spin pumping based on ferromagnetic resonance (FMR) spectroscopy by varying the Pt spacer thickness. Though a powerful method for characterizing the dynamic magnetic properties of FM layers, FMR is seldom the only technique used for investigating spin transport characteristics of asymmetric trilayers. Our analytical focus on the acoustic mode, facilitated by the distinct magnetizations of the Ni80Fe20 and Co layers, allows for the isolation of individual layer resonances. The derived spin pumping induced damping (αsp) of the Ni80Fe20 and Co layers reveals a direct dependence on the Pt spacer thickness. Furthermore, fitting of the weighted average of the damping parameters to the αsp of the acoustic mode reveals that the observed FMR spectra are indeed a result of the in-phase precession of the magnetizations in two FM layers. The extracted effective spin-mixing conductance (geff↑↓) varies with the FM/NM interface, specifically 1.72×1019m-2 at the Ni80Fe20/Pt interface and 4.07×1019m-2 at the Co/Pt interface, indicating a strong correlation with interfacial characteristics. Additionally, we deduce the spin diffusion length in Pt to be between 1.02 and 1.55 nm and calculate the interfacial spin transparency (Tin) and spin current densities, highlighting significant disparities between the Ni80Fe20/Pt and Co/Pt interfaces. This detailed analysis enhances our understanding of the spin transport in Ni80Fe20/Pt/Co trilayers. It offers insights important for advancing spintronic device design and lays the groundwork for future theoretical investigations of asymmetric trilayer systems.