Giant Spin‐Orbit Torque in Sputter‐Deposited Bi Films

Bismuth (Bi) has the strongest spin‐orbit coupling among non‐radioactive elements and is thus a promising material for efficient charge‐to‐spin conversion. However, previous electrical detections have reported controversial results for the conversion efficiency. In this study, an optical detection of a spin‐orbit torque is reported in a Bi/CoFeB bilayer with a polycrystalline texture of (012) and (003). Taking advantage of the optical detection, spin‐orbit torque is accurately separated from the Oersted field and achieves a giant damping‐like torque efficiency of +0.5, verifying efficient charge‐to‐spin conversion. This study also demonstrates a field‐like torque efficiency of −0.1. For the mechanism of the charge‐to‐spin conversion, the bulk spin Hall effect and the interface Rashba‐Edelstein effect are considered.