Spin orbit torque induced asymmetric depinning of chiral Néel domain wall in Co/Ni heterostructures

In this letter, we report on distinct depinning of a chiral Néel domain wall (DW) driven by spin-orbit torque (SOT) in Co/Ni nanowires with symmetric potential barriers. In these structures, DW propagation was shown to be in the opposite direction to the electron flow as evidenced from current assisted DW depinning measurements. A transition from field dominated DW depinning to SOT dominated DW depinning was observed as the bias current was increased. For SOT dominated DW depinning, the Up-Down DW exhibits a larger depinning field as compared to the Down-Up DW. This is attributed to the interplay between the SOT and Dzyaloshinskii-Moriya interaction in the structure

Quantifying orbital Rashba effect via harmonic Hall torque measurements in transition-metal|Cu|Oxide structures

Spin-orbit interaction (SOI) plays a pivotal role in the charge-to-spin conversion mechanisms, notably the spin Hall effect involving spin-dependent deflection of conduction electrons and the interfacial spin Rashba-Edelstein effect. In recent developments, significant current-induced torques have been predicted and observed in material systems featuring interfaces with light elements \textit{i.e.} possessing a weak SOI. These findings challenge existing mechanisms and point to the potential involvement of the orbital counterpart of electrons, namely the orbital Hall and orbital Rashba effects. Here, we establish, in Pt|Co|Cu|AlOx stacking, the comparable strength between the orbital Rashba effect at the Cu|AlOx interface and the effective spin Hall effect in Pt|Co. Subsequently, we investigate the thickness dependence of an intermediate Pt layer in Co|Pt|Cu|CuOx, revealing the strong signature of the orbital Rashba effect at the Cu|CuOx interface besides the well-identified Pt intrinsic spin Hall effect. Leveraging such contribution from the orbital Rashba effect, we show a twofold enhancement in the effective torques on Co through harmonic Hall measurements. This result is corroborated by complementary spin Hall magneto-resistance and THz spectroscopy experiments. Our results unveil unexplored aspects of the electron's orbital degree of freedom, offering an alternative avenue for magnetization manipulation in spintronic devices with potential implications for energy-efficient and environmentally friendly technologies using abundant and light elements.Comment: 11 pages, 5 figure

Role of RKKY torque on domain wall motion in synthetic antiferromagnetic nanowires with opposite spin Hall angles

Abstract We experimentally show the effect of enhanced spin-orbit and RKKY induced torques on the current-induced motion of a pair of domain walls (DWs), which are coupled antiferromagnetically in synthetic antiferromagnetic (SAF) nanowires. The torque from the spin Hall effect (SHE) rotates the Néel DWs pair into the transverse direction, which is due to the fact that heavy metals of opposite spin Hall angles are deposited at the top and the bottom ferromagnetic interfaces. The rotation of both DWs in non-collinear fashion largely perturbs the antiferromagnetic coupling, which in turn stimulates an enhanced interlayer RKKY exchange torque that improved the DW velocity. The interplay between the SHE-induced torque and the RKKY exchange torque is validated via micromagnetic simulations. In addition, the DW velocity can be further improved by increasing the RKKY exchange strength