  Spintronic devices operating with pure spin currents represent a new paradigm
in nanoelectronics, with higher energy efficiency and lower dissipation as
compared to charge currents. This technology, however, will be viable only if
the amount of spin current diffusing in a nanochannel can be tuned on demand
while guaranteeing electrical compatibility with other device elements, to
which it should be integrated in high-density three-dimensional architectures.
Here, we address these two crucial milestones and demonstrate that pure spin
currents can effectively propagate in metallic nanochannels with a
three-dimensional curved geometry. Remarkably, the geometric design of the
nanochannels can be used to reach an independent tuning of spin transport and
charge transport characteristics. These results put the foundation for the
design of efficient pure spin current based electronics, which can be
integrated in complex three-dimensional architectures.
