Field-driven domain wall motion in ferrimagnetic nanowires

Magnetic domain wall (DW) propagation in nanowires is an important problem whose applications require stable high speeds that are very difficult to achieve with ferromagnets due to the existence of the Walker breakdown, which separates a rigid-body motion from an oscillatory motion. One of the recent fascinating discoveries in magnetism is the high-speed DW motion along ferrimagnetic (FiM) nanowires near the angular momentum compensation point (AMCP). A clear understanding of this fascinating phenomenon is still lacking. Here we use the energy conservation principle and generic FiM dynamics to reveal the physics behind the DW motion and the absence of the Walker breakdown and precessional torque at the AMCP. An almost exact DW velocity formula beyond the Walker breakdown field is obtained that agrees with experiments and simulations. This theory provides useful guidance for the design of high-speed spintronic DW devices.