  Despite significant advances in the last decade regarding the room
temperature stabilization of skyrmions or their current induced dynamics, the
impact of local material inhomogeneities still remains an important issue that
impedes to reach the regime of steady state motion of these spin textures.
Here, we study the spin-torque driven motion of skyrmions in synthetic
ferrimagnetic multilayers with the aim of achieving high mobility and reduced
skyrmion Hall effect. We consider Pt|Co|Tb multilayers of various thicknesses
with antiferromagnetic coupling between the Co and Tb magnetization. The
increase of Tb thickness in the multilayers allows to reduce the total magnetic
moment and increases the spin-orbit torques allowing to reach velocities up to
400 m.s-1 for skyrmions with diameters of about 160 nm. We demonstrate that due
to reduced skyrmion Hall effect, combined with the edge repulsion of the
magnetic track making the skyrmions moving along the track without any
transverse deflection. Further, by comparing the field-induced domain wall
motion and current-induced skyrmion motion, we demonstrate that the skyrmions
at the largest current densities present all the characteristics of a dynamical
flow regime.
