Topological damping Rashba spin-orbit torque in ballistic magnetic domain walls

Rashba spin-orbit torque derived from the broken inversion symmetry at ferromagnet/heavy metal interfaces has potential application in spintronic devices. In the conventional description of the precessional and damping components of the Rashba spin-orbit torque in magnetization textures, the decomposition coefficients are assumed to be independent of the topology of the underlying structure. Contrary to this common wisdom, for Schrodinger electrons trespassing ballistically across a magnetic domain wall, we found that the decomposition coefficient of the damping component is determined by the topology of the domain wall. The resultant damping Rashba spin-orbit torque is protected by the topology of the underlying magnetic domain wall and robust against small deviations from the ideal domain-wall profile. Our identification of a topological damping Rashba spin-orbit torque component in magnetic domain walls will help one to understand experiments on current-driven domain-wall motion in ferromagnet/heavy metal systems with broken inversion symmetry and to facilitate its utilization in innovative device designs.