Spin-Wave Emission by Spin-Orbit-Torque Antennas

We study the generation of propagating spin waves in Ta/(Co, Fe) B bilayer waveguides by spin-orbit-torque antennas and compare them with spin waves generated by conventional inductive antennas. The spin-orbit torque is generated by a transverse microwave current across the waveguide. The detected spin-wave signals for a transverse in-plane magnetization (Damon-Eshbach configuration) exhibit the expected phase rotation and amplitude decay on propagation when current spreading is taken into account. Wavevectors up to about 6 rad/mu m can be excited by the spin-orbit-torque antennas despite current spreading, presumably due to the nonuniformity of the microwave current. The relative magnitude of the generated antidamping spin Hall and Oersted fields is calculated with an analytic model and it is found that they contribute approximately equally to the total effective field generated by the spin-orbit-torque antenna. The prospects for obtaining a pure spin-orbit-torque response are discussed, as are the scaling properties of spin-orbit-torque and inductive antennas.