CEM Seminar featuring Andrew Berger: Inductive detection of field-like and damping-like AC inverse spin orbit torques in Py/Pt bilayers

“Inductive detection of field-like and damping-like AC inverse spin orbit torques in Py/Pt bilayers”

Andrew Berger (National Institute of Standards and Technology)

Spin-charge conversion effects are central to functional spintronic devices, and underlie the reciprocal processes of electric field-driven spin torque1 and magnetization dynamics-driven spin and charge flow2–4. There are several mechanisms responsible for spin-charge conversion, varying in their cause (intrinsic or extrinsic), symmetry (field-like or damping-like), and point-of-origin (interfacial or bulk). Both damping-like and field-like spin orbit torques have been observed in the forward process of current-driven spin torque1,5. I will discuss a technique we have developed that uses well-established coplanar waveguide (CPW) ferromagnetic resonance (FMR) for inductive detection of the AC charge currents produced by the inverse spin-charge conversion processes. Time-varying magnetic fields produced by a Py/Pt sample under FMR excitation will inductively couple into the CPW, altering the total inductance of the microwave circuit. Such fields are produced by: (1) the Py precessing magnetization, (2) Faraday effect induced AC currents in the Pt layer, in addition to (3) spin-orbit AC currents due to the spin Hall effect and (4) the Rashba-Edelstein effect. These four terms have distinct frequency dependencies and phase relationships with the driving microwave field such that a phase-sensitive measurement is able to separate them. Our findings reveal that Py/Pt bilayers exhibit both damping-like and field-like inverse spin orbit torques, indicative of bulk spin Hall effect and interfacial Rashba-Edelstein spin-orbit coupling, respectively.