  Neuromorphic computing (NC) is gaining wide acceptance as a potential
technology to achieve low-power intelligent devices. To realize NC, researchers
investigate various types of synthetic neurons and synaptic devices such as
memristors and spintronic domain wall (DW) devices. In comparison, DW-based
neurons and synapses have potentially higher endurance. However, for realizing
low-power devices, DW motion at low energies - typically below pJ/bit - are
needed. Here, we demonstrate domain wall motion at current densities as low as
1E6 A/m2 by tailoring the beta-W spin Hall material. With our design, we
achieve ultra-low pinning fields and current density reduction by a factor of
10000. The energy required to move the domain wall by a distance of about 20
micrometers is 0.4 fJ, which translates into energy consumption of 0.4 aJ/bit
for a bit-length of 20 nm. With a meander domain wall device configuration, we
have established a controlled DW motion for synapse applications and have shown
the direction to make ultra-low energy spin-based neuromorphic elements.
