Dynamics of field-driven domain-wall propagation in ferromagnetic nanowires

Ferromagnetic nanowires are likely to play an important role in future spintronic devices. Magnetic domain walls, which separate regions of opposing magnetization in a nanowire, can be manipulated(1-6) and used to encode information for storage(2,7) or to perform logic operations(1). Owing to their reduced size and dimensionality, the characterization of domain- wall motion is an important problem. To compete with other technologies, high- speed operation, and hence fast wall propagation, is essential. However, the domain- wall dynamics in nanowires has only been investigated(8- 13) in the last. five years and some results indicate a drastic slowing down of wall motion in higher magnetic. fields(8). Here we show that the velocity-. field characteristic of a domain wall in a nanowire shows two linear regimes, with the wall mobility at high. fields reduced tenfold from that at low. fields. The transition is marked by a region of negative differential mobility and highly irregular wall motion. These results are in accord with theoretical predictions that, above a threshold. field, uniform wall movement gives way to turbulent wall motion, leading to a substantial drop in wall mobility(13-19). Our results help resolve contradictory reports of wall propagation velocities in laterally confined geometries(8,9), and underscore the importance of understanding and enhancing the breakdown. field for practical applications.