Excitation and Amplification of Propagating Spin Waves by Spin-Orbit Torque*

Spin-orbit torque (SOT) produced by electric current is among the cornerstones of modern nanomagnetism. However, until now SOT could not be utilized for the generation of propagating spin waves for magnonic (spin wave-based) applications.
We experimentally demonstrate a SOT oscillator directly incorporated into a SOT-enhanced magnonic nano-waveguide. The studied nanostructure is based on a Permalloy(Py)/Pt bilayer patterned into a nanowire forming a spin-wave waveguide, with Py thickness reduced in a narrow notched region of the nanowire. SOT produced by dc electrical current in Pt induces coherent magnetization oscillations in the nano-notch region, emitting spin waves into the nanowire. We utilize spectrally- and spatially-resolved microfocus Brillouin Light Scattering (BLS) measurements to demonstrate unidirectional emission of coherent spin waves, controlled by the direction of the static magnetic field, and simultaneous enhancement of their decay length by SOT. The demonstrated system combines all the advantages provided by the SOT, and can be used as a building block for novel integrated spin-orbit magnonic nano-circuits.
B. Divinskiy et al., Adv. Mater. 30, 1802837 (2018).