Domain-wall circulation gating and pinning via compositional engineering of cylindrical nanowires
Spintronic devices based on cylindrical magnetic nanowires have been proposed as a route toward three-dimensional information storage and processing by harnessing the controlled motion of domain walls (DWs). In this geometry, the Bloch-point wall (BPW) is the characteristic DW type. It features a curling of magnetization around a Bloch Point singularity, a topology that has been predicted to enable propagation at high speed without undergoing a Walker breakdown. We demonstrate that compositional modulations of larger magnetization, which host spontaneous curling states while the rest of the wire remains axial, fulfil a dual role: they act as deterministic pinning sites and as active gates for BPW circulation. Combining magnetic transmission X-ray microscopy and micromagnetic simulations, we reveal that DW-modulation interactions are the result of a superposition of long-range magnetostatic repulsion and short-range, circulation-dependent exchange contributions: parallel circulation produces an attractive well, while opposite circulation generates a repulsive barrier. This results in DW pinning at or near a compositional modulation. A DW's internal circulation can be inverted upon traversing a modulation, enabling on-demand switching of its circulation state. This dual mechanism demonstrates that both DW position and circulation can be tuned in a controlled manner, with potential implications for multistate spintronic devices.