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

Abstract

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^1,2,3,4,5,6 and used to encode information for storage^2,7 or to perform logic operations¹. 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^{8,9,10,11,12,13} in the last five years and some results indicate a drastic slowing down of wall motion in higher magnetic fields⁸. 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^{13,14,15,16,17,18,19}. 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.