Efficient orbital current generation in nitrided Cu

Spin-orbit torque memory is realized as a promising technique for next generation memory and neuromorphic applications. In principle, the sizable SOT is believed to originate from strong spin-orbit coupling (SOC) in heavy metals, topological insulators, and Weyl semimetals. However, recent reports suggest that the light metals can also generate non-negligible SOTs and these SOC-free torques are attributed to the orbital angular momentum induced orbital currents. In this work, we investigate the orbital currents generation in nitrided Cu. We prepare the Pt/Co/CuN_x perpendicular magnetic heterostructures and introduce nitrogen into Cu capping layer via reactive sputtering. The hysteresis loop shift measurement confirms that the charge-to-spin conversion efficiency can be enhanced from 2% to ~ 40% through controlling the doping concentration. This significant enhancement is attributed to the orbital currents generated by the nitrided Cu capping layer. Furthermore, we demonstrate the neuromorphic switching measurement, and the multistate behavior shows that the orbital currents can effectively manipulate the perpendicular magnetization. These results provide valuable information for building energy-efficient spin-orbitronic neuromorphic devices.