Spin pumping at interfaces with ferro- and paramagnetic Fe60Al40 films acting as spin source and spin sink

We present a study of spin pumping efficiency and determine the spin mixing conductance and spin diffusion length in thin bilayer films based on 3d transition metal alloy Fe60Al40. Due to its magnetostructural phase transition, Fe60Al40 can be utilized as a ferromagnetic (FM) or paramagnetic (PM) material at the same temperature depending on its structural order; thus a thin Fe60Al40 film can act as a spin source or a spin sink when interfaced with a paramagnet or a ferromagnet, respectively. Ferromagnetic resonance measurements were performed in a frequency range of 5–35 GHz on bilayer films composed of FM–Fe60Al40/Pd and PM–Fe60Al40/Ni80Fe20 (permalloy). The increase in damping with the thickness of the paramagnetic layer was interpreted as a result of spin pumping into the paramagnet. We determine the spin mixing conductance gPd↑↓=(3.8±0.5)×1018m−2 at the FM–Fe60Al40/Pd interface and the spin diffusion length λPd=9.1±2.0nm in Pd. For the PM–Fe60Al40/permalloy interface, we find a spin mixing conductance gFeAl↑↓=(2.1±0.2)×1018m−2 and a spin diffusion length λFeAl=11.9±0.2nm for PM–Fe60Al40. The demonstrated bi-functionality of the Fe60Al40 alloy in spin pumping structures may be promising for spintronic applications.