  A storage scheme based on racetrack memory, where the information can be
coded in a domain or a skyrmion, seems to be an alternative to conventional
hard disk drive for high density storage. Here, we perform a full micromagnetic
study of the performance of synthetic antiferromagnetic (SAF) racetrack memory
in terms of velocity and sensitivity to defects by using experimental
parameters. We find that to stabilize a SAF skyrmion, the Dzyaloshinskii-Moriya
Interaction in the top and the bottom ferromagnet should have an opposite sign.
The velocity of SAF skyrmion and SAF Neel domain wall are of the same order and
can reach values larger than 1200 m/s if a spin-orbit torque from the spin-Hall
effect with opposite sign is applied to both ferromagnets.
