Three-dimensional nanostructured magnetic materials have recently been the topic of intense interest since they provide access to a host of new physical phenomena. Examples include new spin textures that exhibit topological protection, magnetochiral effects and novel ultrafast magnetic phenomena such as the spin-Cherenkov effect. Two-photon lithography is a powerful methodology that is capable of realising 3D polymer nanostructures on the scale of 100 nm. Combining this with postprocessing and deposition methodologies allows 3D magnetic nanostructures of arbitrary geometry to be produced. In this article, the physics of two-photon lithography is first detailed, before reviewing the studies to date that have exploited this fabrication route. The article then moves on to consider how non-linear optical techniques and post-processing solutions can be used to realise structures with a feature size below 100 nm, before comparing two-photon lithography with other direct write methodologies and providing a discussion on future developments.

Cylindrical magnetic nanowires have been shown to exhibit a vast array of fascinating spin textures, including chiral domains, skyrmion tubes, and topologically protected domain walls that harbor Bloch points. Here, we present a novel methodology that utilizes two-photon lithography in order to realize tailored three-dimensional (3D) porous templates upon prefabricated electrodes. Electrochemical deposition is used to fill these porous templates, and reactive ion etching is used to free the encased magnetic nanowires. The nanowires are found to have a diameter of 420 nm, length of 2.82 μm, and surface roughness of 7.6 nm. Magnetic force microscopy in an externally applied field suggests a complex spiraling magnetization state, which demagnetizes via the production of vortices of alternating chirality. Detailed micro-magnetic simulations confirm such a state and a qualitative agreement is found with respect to the switching of experimental nanowires. Surprisingly, simulations also indicate the presence of a Bloch point as a metastable state during the switching process. Our work provides a new means to realize 3D magnetic nanowires of controlled geometry and calculations suggest a further reduction in diameter to sub-200 nm will be possible, providing access to a regime of ultrafast domain wall motion.

Cylindrical magnetic nanowires have been studied extensively over the past ten years due to the presence of domain walls with novel topology and outstanding dynamic properties. In soft magnetic systems, where shape anisotropy forces the magnetization along the wire axis, and for radii above 50 nm, two topologically distinct walls have been previously identified. The Bloch point wall (BPW) has a circulating magnetization texture around the circumference and contains a single Bloch point within the center of the wire cross section. In contrast, asymmetric transverse walls (ATWs) have a circulating magnetization structure on the surface and contain two topological defects, a vortex and an anti-vortex on opposing sides. These surface defects are connected via a vortex tube that penetrates the volume. In this study, we have numerically investigated the domain wall magnetization textures for nickel nanowires of radii 50–120 nm. Beyond reproducing the known BPW and ATW topology, we discover a new domain wall type that contains aspects of both. This new domain wall type, which we call asymmetric dual Bloch point wall (ADBPW), has surface vortices similar to an ATW and two Bloch-point textures adjacent to the internal vortex tube. Time-resolved simulations investigating the stability of ADBPW show its field-driven transformation into a BPW via the ejection of a single Bloch point at the surface and subsequent annihilation of surface vortices.