Spin pumping in embedded lateral nanostructures in Fe60Al40

Abstract

We report on ferromagnetic resonance (FMR) detected spin pumping in Fe60Al40/Pd and Py/Fe60Al40 bilayer and laterally patterned Fe60Al40 nanostructures. The magnetic properties of Fe60Al40 alloy are easily tailorable from paramagnetic to ferromagnetic state by variation of the structure through ion beam irradiation, making a promising material for the fabrication of magnetic landscapes and magnonic crystals [1,2]. Exploiting this easy tunability we show that Fe60Al40 can be used as well as spin source as spin sink in spin pumping experiments. Using the material with the identical chemical composition leads to a new pathway creating geometries for lateral spin pumping and might lead to an increase in efficiency in spin pumping as the writing of structures using ion beam irradiation allows to realize spin-based binary logic systems.Characteristic quantities to estimate the efficiency of spintronic systems are the spin mixing conductance and the spin diffusion length determined by thickness and frequency dependent FMR measurements [3]. Therefore, two sets of bilayer samples consisting of ferromagnetic (FM) and paramagnetic (PM) layers have been prepared, i.e. FM Fe60Al40 films of 5 nm thickness capped with Pd of varying thickness as well as Py of 5 nm thickness capped with PM Fe60Al40 of varying thickness. They were investigated using frequency dependent FMR measurements in a range of 2 to 35 GHz.The FMR linewidth and damping analysis reveal a spin mixing conductance of g↑↓ = (2.092 ± 0.046)×1018 m-2 and a spin diffusion length of λFeAl = 17.2 ± 0.86 nm (see Fig. 1) for paramagnetic Fe60Al40, and g↑↓ = (4.454 ± 0.0479)×1018 m-2 and λPd = 8.513 ± 1.631 nm nm for Pd. Based on a result of the determined efficiency of Fe60Al40 used as spin source and spin sink, we investigate the spin pumping in laterally patterned Fe60Al40 nanostructures (see Fig. 2) representing 500 nm wide stripes of FM Fe60Al40 separated with PM Fe60Al40 stripes of different width (100-400 nm) produced in 40 nm thick film, which demonstrate a decrease of the damping parameter with increasing width of PM Fe60Al40 areas. **