Theory of staggered damping-like spin-orbit torque on synthetic antiferromagnetic domain walls

RESUMO

The Néel, or staggered, spin-orbit torque (SOT) enables an efficient electrical manipulation of antiferromagnetic order. However, it has been tied to special crystal structures, and only its field-like component is established. We develop a theory of staggered damping-like SOT, which arises generically in synthetic antiferromagnets sandwiched by the same heavy metal on both sides. Deriving a Néel-vector Lagrangian, we obtain the domain-wall (DW) velocity in closed form: bilinear in current and in-plane field, opposite in sign for Néel and Bloch walls, and tunable through the interlayer exchange coupling. DW structure thus becomes a control knob for DW motion, while the DW motion, in turn, offers an electrical readout of its structure. Micromagnetic simulations confirm the theory. The predicted sign reversals and scaling laws of the DW velocity, together with the thresholds for the Néel-Bloch transition, give immediate experimental targets.