Reduced Switching Current with a Light Metal in a Tri-layer Spin-orbit Torque Device

The use of a tri-layer structure and light metals have each received much research attention in spin-orbit torque (SOT) technology. We combine these two approaches by placing an ultra-thin (1 nm) Cu adjacent to the bottom ferromagnetic layer in a tri-layer SOT device. This can reduce the switching current by ~30% compared to the conventional bi-layer device due to enhanced SOT efficiency. This advantage is more obvious under a unipolar condition and it is attributed to a slightly asymmetric interface caused by the Cu insertion. By magneto-optical Kerr effect microscopy, we also observe a domain reversal mechanism distinct from the bi-layer case.