Ferromagnetic resonance studies of accumulation and diffusion of spin momentum density in Fe/Ag/Fe/GaAs(001) and Ag/Fe/GaAs(001) structures

Spin transport was investigated in magnetic single GaAs/16 Fe/mAg/20 Au(001) and double GaAs/16 Fe/nAg/12 Fe/20 Au(001) layer structures prepared by molecular-beam epitaxy, where m = 0, 5, 20, 1500 and n = 20, 100, 300, 500, 1500. The integers represent the number of Fe, Ag, and Au atomic layers, respectively. The set of Ag spacers in magnetic double layers allowed one to investigate nonlocal spin transport from ballistic to fully developed spin-diffusion limit. The spin transport in these structures was investigated using spin pumping effect at the 16Fe/Ag(001) interface. Ferromagnetic resonance (FMR) studies were carried out using standard microwave spectrometers at 9, 36, and 72 GHz. The FMR linewidth Delta H in the above structures was found to follow Gilbert damping mechanism. The measured Delta H as a function of the Ag spacer thickness in GaAs/16 Fe/n Ag/12 Fe/20 Au(001) was interpreted using Kirchhoff's laws for spin electronics which includes the spin diffusion across the Ag spacer allowing one to determine the electron charge and spin-flip time scattering parameters and the spin-diffusion length in the Ag thin-film spacers.