  Current-induced spin-orbit torque (SOT) is regarded as a promising mechanism
for driving neuromorphic behavior in spin-orbitronic devices. In principle, the
strong SOT in heavy metal-based magnetic heterostructure is attributed to the
spin-orbit coupling (SOC)-induced spin Hall effect (SHE) and/or the spin
Rashba-Edelstein effect (SREE). Recently, SOC-free mechanisms such as the
orbital angular momentum (OAM)-induced orbital Hall effect (OHE) and/or the
orbital Rashba-Edelstein effect (OREE) have been proposed to generate sizable
torques comparable to those from the conventional spin Hall mechanism. In this
work, we show that the orbital current can be effectively generated by the
nitrided light metal Cu. The overall damping-like SOT efficiency, which
consists of both the spin and the orbital current contributions, can be
tailored from ~ 0.06 to 0.4 in a Pt/Co/CuNx magnetic heterostructure by tuning
the nitrogen doping concentration. Current-induced magnetization switching
further verifies the efficacy of such orbital current with a critical switching
current density as low as Jc ~ 5 x 10^10 A/m2. Most importantly, the
orbital-current-mediated memristive switching behavior can be observed in such
heterostructures, which reveals that the gigantic SOT and efficient
magnetization switching are the tradeoffs for the applicable window of
memristive switching. Our work provides insights into the role of orbital
current might play in SOT neuromorphic devices and paves a new route for making
energy-efficient spin-orbitronic devices.
