Design and control of three-dimensional topological magnetic fields using interwoven helical nanostructure

Three-dimensional (3D) magnetic nanostructures are an emerging tool for the creation of topological magnetic fields on the nanoscale [1, 2]. The control of these localized magnetic fields is seen to be of importance in applications for particle trapping and drug delivery [3, 4]. Focused electron beam induced deposition (FEBID) enables the experimental realization of functional 3D magnetic nanostructures through utilizing software like f3ast [5]. The patterned 3D geometric curvature and proximity can allow the formation of intricate spin textures, not possible in two-dimensions, which can be further altered through applied magnetic fields [1, 6, 7]. This geometric control of magnetization can allow the design of unique and reconfigurable topological stray field patterns. In this work, we will outline the controlled formation of several topological stray field textures enabled by reconfiguring the magnetization in a 3D nanostructure. We will show complementary experimental and micromagnetic studies of nanostructures formed by several interwoven helical nanowires fabricated by FEBID and characterized by off-axis electron holography. Through the application of a global magnetic field, we can form multi-domain or single domain magnetic states. Consequently, corresponding arrangements of magnetic charges will arise throughout the nanostructure, leading to unique forms of the emanating stray field. Using this method, we show the formation of a sixfold multipole field cusp, an anti-vortex field and a skyrmion tube-like stray field pattern. These results show a further development of how 3D nanostructures could be utilized in the creation of topological magnetic field textures and provide insight into how they can be controllably reconfigured and designed.