  Building nanotechnological analogues of naturally occurring magnetic
structures has proven to be a powerful approach to studying topics like
geometry-induced magnetic frustration and to provide model systems for
statistical physics. Moreover, it practically allows to engineer novel physical
properties by realizing artificial lattice geometries that are not accessible
via natural crystallization or chemical synthesis. This has been accomplished
with great success in the field of two-dimensional artificial spin ice systems
with important branches reaching into the field of magnetic logic devices.
Although first proposals have been made to advance into three dimensions (3D),
established nanofabrication pathways based on electron beam lithography have
not been adapted to obtain free-form 3D nanostructures. Here we demonstrate the
direct-write fabrication of freestanding ferromagnetic 3D nano-architectures
with full control over the degree of magnetic frustration. By employing
micro-Hall sensing, we have determined the magnetic stray field generated by
our free-form structures in an externally applied magnetic field and we have
performed micromagnetic and macro-spin simulations to deduce the spatial
magnetization profiles in the structures and analyze their switching behavior.
Furthermore we show that the magnetic 3D elements can be combined with other 3D
elements of different chemical composition and intrinsic material properties.
