Large Interfacial Rashba Interaction Generating Strong Spin-Orbit Torques in Atomically Thin Metallic Heterostructures

The hallmark of spintronics has been the ability of spin-orbit interactions to convert a charge current into a spin current and vice versa, mainly in the bulk of heavy metal thin films. Here, we demonstrate how a light metal interface profoundly affects both the nature of spin-orbit torques and its efficiency in terms of damping-like (H_DL) and field-like (H_FL) effective fields in ultrathin Co films. We measure unexpectedly H_FL/H_DL ratios much larger than 1 by inserting a nanometer-thin Al metallic layer in Pt|Co|Al|Pt as compared to a similar stacking, including Cu as a reference. From our modeling, these results evidence the existence of large Rashba interaction at the Co|Al interface generating a giant H_FL, which is not expected from a metallic interface. The occurrence of such enhanced torques from an interfacial origin is further validated by demonstrating current-induced magnetization reversal showing a significant decrease of the critical current for switching.