  We report on a theoretical study of the spin-current excited dynamics of
domain walls (DWs) in ferrimagnets in the vicinity of the angular momentum
compensation point. Effective Lagrangian and nonlinear dynamic equations are
derived for a two-sublattice ferrimagnet taking into account both spin-torques
and external magnetic field. The dynamics of the DW before and after the Walker
breakdown is calculated for any direction of the spin current polarization. It
is shown that for the in-plane polarization of the spin current, the DW
mobility reaches a maximum near the temperature of the angular momentum
compensation. For the out-of-plane spin polarization, in contrast, a spin
current with the densities below the Walker breakdown does not excite the
dynamics of the DW. After overcoming the Walker breakdown, the domain wall
velocity increases linearly with increasing the current density. In this
spin-current polarization configuration the possibility of a gigahertz
oscillation dynamics of the quasi-antiferromagnetic vector under the action of
a damping-like torque in the angular momentum compensation point is
demonstrated. Possible structures for experimental demonstration of the
considered effects are discussed.
