Spin-wave amplification using spin-orbit torque in ultra-thin BiYIG/Pt microscopic waveguide

In this work we report the first experimental observation of the amplification of rf-excited propagating spin-waves (SW) based on spin-orbit torque (SOT), in a 500nm wide Bi₁YIG/Pt waveguide using micro Brillouin light scattering spectroscopy.

By applying a dc current in the Pt, the effective damping is decreased due to the SOT that compensate the Gilbert damping. Once the current reaches a threshold value, the vanishing effective damping allows for the onset of the auto-oscillation (AO) regime. However, SWs strongly interact with the AO, preventing their amplification (as similarly observed in other studies). Using an rf and DC pulse scheme, we propagate rf-excited SWs before the onset of non-linearities and observe their clear amplification. Above the critical current, the SW intensity exponentially increases with the propagation distance (negative effective damping), up to a 12 µm amplification length (corresponding to a 5 time increase in intensity over 10 µm). Furthermore, we evidence the key role of the vanishing effective magnetization of the BiYIG film that suppresses the non-linear interactions that have so far prevented the amplification of propagating SWs using SOT.

This experiment sheds new light on the influence of SOT on propagating SWs and pave the way toward an efficient magnonic amplifier using DC current.