Combining two-photon lithography with laser ablation of sacrificial layers: A route to isolated 3D magnetic nanostructures

Three-dimensional (3D) nanostructured functional materials are important systems allowing new means for intricate control of electromagnetic properties. A key problem is realising a 3D printing methodology on the nanoscale that can yield a range of functional materials. In this article, it is shown that two-photon lithography, when combined with laser ablation of sacrificial layers, can be used to realise such a vision and produce 3D functional nanomaterials of complex geometry. Proof-of-principle is first shown by fabricating planar magnetic nanowires raised above the substrate that exhibit controlled domain wall injection and propagation. Secondly, 3D artificial spin-ice (3DASI) structures are fabricated, whose complex switching can be probed using optical magnetometry. We show that by careful analysis of the magneto-optical Kerr effect signal and by comparison with micro-magnetic simulations, depth dependent switching information can be obtained from the 3DASI lattice. The work paves the way for new materials, which exploit additional physics provided by non-trivial 3D geometries.