  We measured the spin-orbit torques (SOTs), current-induced switching, and
domain wall (DW) motion in synthetic ferrimagnets consisting of Co/Tb layers
with differing stacking order grown on a Pt underlayer. We find that the SOTs,
magnetic anisotropy, compensation temperature and SOT-induced switching are
highly sensitive to the stacking order of Co and Tb and to the element in
contact with Pt. Our study further shows that Tb is an efficient SOT generator
when in contact with Co, such that its position in the stack can be adjusted to
generate torques additive to those generated by Pt. With optimal stacking and
layer thickness, the dampinglike SOT efficiency reaches up to 0.3, which is
more than twice that expected from the Pt/Co bilayer. Moreover, the
magnetization can be easily switched by the injection of pulses with current
density of about 0.5-2*107A/cm2 despite the extremely high perpendicular
magnetic anisotropy barrier (up to 7.8 T). Efficient switching is due to the
combination of large SOTs and low saturation magnetization owing to the
ferrimagnetic character of the multilayers. We observed current-driven DW
motion in the absence of any external field, which is indicative of homochiral
N\'eel-type DWs stabilized by the interfacial Dzyaloshinkii-Moriya interaction.
These results show that the stacking order in transition metal/rare-earth
synthetic ferrimagnets plays a major role in determining the magnetotransport
properties relevant for spintronic applications.
