Tailoring neuromorphic switching by CuNx-mediated orbital currents

Abstract: 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.