Enhanced second harmonic Hall resistance in in-plane synthetic antiferromagnets

Synthetic antiferromagnet (SyAF) has been demonstrated to be an ideal candidate for spin–orbit torque (SOT) based spintronic devices. However, the detailed mechanism needs to be clarified due to the coexistence of multiple effects. This paper studies SOT and the thermoelectric effect in SyAF of Pt/Co/Ru/Co/Pt by harmonic Hall resistance measurements. Different from the traditional Co/Pt bilayers, the second harmonic Hall resistance signals of the SyAF-based devices are obviously enhanced under a large external magnetic field (Bext), which is caused by the antiferromagnetic exchange coupling fields weakening the influence of Bext. By fitting the Hall resistance curves, the field-like torque is demonstrated to be the main contribution to the Hall resistance. Interestingly, both the SOT effective fields are greatly enhanced for antiparallel alignment. This study separates the contributions of SOT and the thermoelectric effect in the SyAF structures and enables the design of the spintronic devices with stability under a large magnetic field.