  The fascinating high-speed field-driven domain wall (DW) motion along
ferrimagnetic nanowires near the angular momentum compensation point (AMCP) is
solved based on the generic ferrimagnetic dynamics. The physics of the absences
of precessional torque and infinite high Walker breakdown field at the AMCP is
proved under general conditions. Based on the energy conservation principle, an
almost exact DW velocity formula, valid beyond the Walker breakdown field, is
obtained. Our results agree with all existing experiments and simulations. This
theory provides useful guidances to DW manipulation.
