  Unidirectional motion of magnetic domain walls is the key concept underlying
next-generation domain-wall-mediated memory and logic devices. Such motion has
been achieved either by injecting large electric currents into nanowires or by
employing domain-wall tension induced by sophisticated structural modulation.
Herein, we demonstrate a new scheme without any current injection or structural
modulation. This scheme utilizes the recently discovered chiral domain walls,
which exhibit asymmetry in their speed with respect to magnetic fields. Because
of this asymmetry, an alternating magnetic field results in the coherent motion
of the domain walls in one direction. Such coherent unidirectional motion is
achieved even for an array of magnetic bubble domains, enabling the design of a
new device prototype-magnetic bubblecade memory-with two-dimensional
data-storage capability.
