Phase-Sensitive Detection of Spin Pumping via the ac Inverse Spin Hall Effect
Thomas J. Silva, Justin M. Shaw, Hans T. Nembach, Mathias A. Weiler
Sources of pure spin currents are a fundamental building block of spintronic devices. In ferromagnet/normal metal heterostructures, spin currents are generated at ferromagnetic resonance. This is known as spin pumping, where spin currents of both dc and ac character diffuse from the ferromagnet into the normal metal, causing an enhancement of magnetization damping. Thereby, in the small magnetization excitation limit, ac spin currents dominate over their dc counterparts. Thus, spin pumping can provide a viable source of ac spin currents in the application-relevant microwave regime. For the detection of dc spin currents, the inverse spin Hall effect in the normal metal has been the method of choice, as it allows for an all-electrical detection of angular momentum flow. However, this electrical detection scheme cannot be applied to microwave spin current detection without taking inductive ac voltages due to the precessing magnetization into account. We here experimentally demonstrate a scheme for the phase-sensitive detection and separation of ac iSHE and inductive signals.