Spin-orbit torques for current parallel and perpendicular to a domain wall

TL;DR

This study investigates how spin-orbit torques influence domain wall depinning in nanowires, revealing that current direction relative to the wall has similar efficiency, dominated by damping-like torque, with depinning efficiency depending on wall structure and pinning sites.

Contribution

First experimental comparison of domain wall depinning efficiency for currents parallel and perpendicular to the wall, highlighting the role of damping-like spin-orbit torque and structural sensitivity.

Findings

Maximum depinning efficiency similar for both current directions

Depinning efficiency depends on domain wall structure and pinning sites

Damping-like spin-orbit torque dominates depinning behavior

Abstract

We report field- and current-induced domain wall (DW) depinning experiments in Ta/Co20Fe60B20/MgO nanowires through a Hall cross geometry. While purely field-induced depinning shows no angular dependence on in-plane fields, the effect of the current depends crucially on the internal DW structure, which we manipulate by an external magnetic in-plane field. We show for the first time depinning measurements for a current sent parallel to the DW and compare its depinning efficiency with the conventional case of current flowing perpendicularly to the DW. We find that the maximum efficiency is similar for both current directions within the error bars, which is in line with a dominating damping-like spin-orbit torque (SOT) and indicates that no large additional torques arise for currents parallel to the DW. Finally, we find a varying dependence of the maximum depinning efficiency angle for different DWs and pinning levels. This emphasizes the importance of our full angular scans compared to previously used measurements for just two field directions (parallel and perpendicular to the DW) and shows the sensitivity of the spin-orbit torque to the precise DW structure and pinning sites.