Domain Wall Pumping with Spin-Transfer Torque

We numerically investigate the effects of current-perpendicular-to-the-plane (CPP), angularly asymmetric Slonczewski spin-transfer torque (ST) on transverse domain walls (DW) in nanowires. The CPP ST excites long-range domain wall motion in a direction independent of the current polarity and proportional to the square of the current amplitude. This symmetry with respect to current polarity creates the possibility of DW pumping -- long range DW motion driven by an alternating current. The DW velocity becomes resonantly enhanced near a frequency that depends on the nanowire dimensions, corresponding to the eigenfrequency of a localized, spatially antisymmetric spin-wave mode that exists within the DW.