Magnetic bubblecade memory

For next-generation memory and logic devices, there have been suggested many concepts of the unidirectional coherent motion of magnetic domain walls (DWs) [1-3]. Such motion occurs either by injecting large electric currents into nanowires [1] or by employing DW tension induced by sophisticated structural modulation [2, 3]. These schemes, however, require either a high threshold [1] or highly sophisticated nanofabrication processes. Here, we demonstrate a new scheme for unidirectional DW motion without any current injection or structural modulation. This scheme utilizes the recently discovered chiral DWs, due to the Dzyaloshinskii-Moriya interaction, which exhibit asymmetry in their speed with respect to magnetic fields [4]. Because of this asymmetry, an alternating magnetic field results in a coherent motion of the domain walls in one direction. For a proof-of-principle experiment, an arbitrary 5×5 array pattern of bubbles (Fig. 1a) is initially created on the film using the thermomagnetic writing method [5]. Under the application of alternating magnetic pulses, all bubbles exhibit coherent unidirectional motion, as shown by the sequential images (Figs. 1b-d and see Ref. [5]) captured during the pulses. Interestingly, the bubble-array pattern is exactly maintained even after traveling more than 1 mm (Fig. 1d). The observed coherent unidirectional motion of the bubbles possibly replaces the mechanical motion of the magnetic media, enabling a new device prototype - magnetic bubblecade memory - with two-dimensional data-storage capability.