Domain Wall Motion and the Interfacial Dzyaloshinskii-Moriya Interaction in Pt/Co/RuO2(Ru) Multilayers.

The interfacial Dzyaloshinskii-Moriya interaction (DMI) plays a pivotal role in stabilising and controlling the motion of chiral spin textures, such as Néel-type bubble domains, in ultrathin magnetic films-an essential feature for next-generation spintronic devices. In this work, we investigate domain wall (DW) dynamics in magnetron-sputtered Ta(3 nm)/Pt(3 nm)/Co(1 nm)/RuO2(1 nm) [Ru(1 nm)]/Pt(3 nm) multilayers, benchmarking their behaviour against control stacks. Vibrating sample magnetometry (VSM) was employed to determine saturation magnetisation and perpendicular magnetic anisotropy (PMA), while polar magneto-optical Kerr effect (P-MOKE) measurements provided coercivity data. Kerr microscopy visualised the expansion of bubble-shaped domains under combined perpendicular and in-plane magnetic fields, enabling the extraction of effective DMI fields. Brillouin light scattering (BLS) spectroscopy quantified the asymmetric propagation of spin waves, and micromagnetic simulations corroborated the experimental findings. The Pt/Co/RuO2 system exhibits a Dzyaloshinskii-Moriya interaction (DMI) constant of ≈1.08 mJ/m2, slightly higher than the Pt/Co/Ru system (≈1.03 mJ/m2) and much higher than the Pt/Co control (≈0.23 mJ/m2). Correspondingly, domain walls in the RuO2-capped films show pronounced velocity asymmetry under in-plane fields, whereas the symmetric Pt/Co/Pt shows negligible asymmetry. Despite lower depinning fields in the Ru-capped sample, its domain walls move faster than those in the RuO2-capped sample, indicating reduced pinning. Our results demonstrate that integrating RuO2 significantly alters interfacial spin-orbit interactions.