Field-induced demagnetisation of bisegmented cylindrical ferromagnetic nanowires mediated by skyrmion tubes

Cylindrical magnetic nanowires offer exciting possibilities for potential applications in spintronic devices that rely on manipulation of topologically non-trivial three-dimensional domain walls. This work investigates field-induced magnetisation processes in bisegmented FeCo nanowires, with sharp diameter modulation, specially designed for the controlled nucleation of magnetic domain walls. By employing variable-field magnetic force microscopy techniques and micromagnetic simulations, we observe that domain wall nucleation, specifically of the Bloch-point type, is mediated by an intermediate skyrmion tube texture that closes the stray field lines, making it detectable by a magnetic force microscopy probe. The simulations further demonstrate that domain wall motion is chirality-dependent; domain walls with non-aligned chirality relative to the direction of spin precession are halted by the emission of surface spin waves, which also switch the domain wall chirality. In the case of aligned chirality, domain walls propagate freely. These findings provide novel insight into the nucleation, stabilization, and motion of complex domain wall textures in cylindrical nanowires and contribute to the understanding of curvature-dependent magnetic phenomena, with implications for designing high-speed domain wall-based devices.