  Bio-inspired hardware holds the promise of low-energy, intelligent and highly
adaptable computing systems. Applications span from automatic classification
for big data management, through unmanned vehicle control, to control for
bio-medical prosthesis. However, one of the major challenges of fabricating
bio-inspired hardware is building ultra-high density networks out of complex
processing units interlinked by tunable connections. Nanometer-scale devices
exploiting spin electronics (or spintronics) can be a key technology in this
context. In particular, magnetic tunnel junctions are well suited for this
purpose because of their multiple tunable functionalities. One such
functionality, non-volatile memory, can provide massive embedded memory in
unconventional circuits, thus escaping the von-Neumann bottleneck arising when
memory and processors are located separately. Other features of spintronic
devices that could be beneficial for bio-inspired computing include tunable
fast non-linear dynamics, controlled stochasticity, and the ability of single
devices to change functions in different operating conditions. Large networks
of interacting spintronic nano-devices can have their interactions tuned to
induce complex dynamics such as synchronization, chaos, soliton diffusion,
phase transitions, criticality, and convergence to multiple metastable states.
A number of groups have recently proposed bio-inspired architectures that
include one or several types of spintronic nanodevices. In this article we show
how spintronics can be used for bio-inspired computing. We review the different
approaches that have been proposed, the recent advances in this direction, and
the challenges towards fully integrated spintronics-CMOS (Complementary metal -
oxide - semiconductor) bio-inspired hardware.
