  Three-dimensional nanostructured functional materials are important systems,
allowing new means to intricately control electromagnetic properties. A key
problem is realising a 3D printing methodology upon the nanoscale that can
yield a range of functional materials. In this letter, it is shown that
two-photon lithography when combined with femtosecond machining of sacrificial
layers, can be used to realise such a vision and produce 3D functional
nanomaterials of complex geometry. This is demonstrated by fabricating 3D
magnetic nanowires that exhibit controlled domain wall injection and
propagation. Secondly, we fabricate large scale 3D artificial spin-ice
structures 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 to
new materials, which exploit additional physics provided by non-trivial 3D
geometries.
