A study of tailored domain wall geometries in ferromagnetic nanowires using Lorentz microscopy

This work presents results on the degree of asymmetry in Transverse Domain Walls (TDWs) by means of micro-magnetic simulation and Lorentz microscopy. Here, head-to-head (H2H)-TDWs were simulated in straight permalloy(Py)-Ni80Fe20nanowires. This aims to explore how to define symmetry and asymmetry of TDWs via quantitative measurement of symmetry/asymmetry as described by a correlation between magnetization components (Mx, My) and region areas (A1, A2) inside TDWs. Experimentally, curved nanowires of differing widths were patterned by Focussed-Ion-Beam (FIB) irradiation. Lorentz microscopy experiments indicate that the degree of asymmetry of TDWs in the curved nanowires is strongly affected by structural effects, i.e. degree of edge roughness. Our results are a new route-map of quantitative measurement for transition between symmetric and asymmetric TDWs. The results are helpful for the determination of TDW configurations in the static state after the application of a magnetic field orelectrical current pulse when TDWs are driven by magnetic field or current. Indeed, our results may support a greater understanding of DW creation and propagation in magnetic nanowires which are of interest for concepts of high-density and ultrafast nonvolatile data storage devices such as racetrack memory and magnetic logic gates.