  Recent progress in nanofabrication has led to the emergence of
three-dimensional magnetic nanostructures as a vibrant field of research. This
includes the study of three-dimensional arrays of interconnected magnetic
nanowires with tunable artificial spin-ice properties. Prominent examples of
such structures are magnetic buckyball nanoarchitectures, which consist of
ferromagnetic nanowires connected at vertex positions corresponding to those of
a C60 molecule. These structures can be regarded as prototypes for the study of
the transition from two- to three-dimensional spin-ice lattices. In spite of
their significance for three-dimensional nanomagnetism, little is known about
the micromagnetic properties of buckyball nanostructures. By means of
finite-element micromagnetic simulations, we investigate the magnetization
structures and the hysteretic properties of several sub-micron-sized magnetic
buckyballs. Similar to ordinary artificial spin ice lattices, the array can be
magnetized in a variety of zero-field states with vertices exhibiting different
degrees of magnetic frustration. Remarkably, and unlike planar geometries,
magnetically frustrated states can be reversibly created and dissolved by
applying an external magnetic field. This easiness to insert and remove
defect-like magnetic charges, made possible by the angle-selectivity of the
field-induced switching of individual nanowires, demonstrates a potentially
significant advantage of three-dimensional nanomagnetism compared to planar
geometries. The control provided by the ability to switch between ice-rule
obeying and magnetically frustrated structures could be an important feature of
future applications, including magnonic devices exploiting differences in the
fundamental frequencies of these configurations.
