Magnetic Domain Wall Pumping by Spin Transfer Torque

We show that spin transfer torque from a direct spin-polarized current applied parallel to a magnetic domain wall (DW) induces DW motion in a direction independent of the current polarity. This unidirectional response of the DW to spin torque enables DW pumping-long-range DW displacement driven by an alternating current. Our numerical simulations reveal that DW pumping can be resonantly amplified through excitation of internal degrees of freedom of the DW by the current.