Spin Pumping in Permalloy/Graphene and Permalloy/Graphite Interfaces

This article reports a comparative study of the spin pumping induced by graphite and graphene layers adjacent to an extended ferromagnetic Permalloy film. The corresponding enhancement of the Gilbert damping in the ferromagnet is determined by analyzing the frequency dependence of the ferromagnetic resonance linewidth in experiments done with a broad band microwave spectrometer. The results show that a single graphene layer is more efficient than a thick graphite film in absorbing the angular momentum pumped away from the Permalloy during the resonant precession of its magnetization. We associate this effect to an enhancement of the spin-orbit coupling in the graphene layer due to Copper adatoms residual from the chemical vapor deposition process used to synthesize the graphene used in the experiments.