Field-driven dynamics of domain walls

in ferromagnetic nanowires

PAPER: G. S. D. Beach, C. Nistor, C. Knutson, M. Tsoi, & J. L. Erskine, “Dynamics of field-driven domain-wall propagation in ferromagnetic nanowires”, Nature Materials 4, 741 (2005)

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 [1–6] 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 [8–13] 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.

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This work was supported by the NSF (NIRT program) under DMR-0404252 and by the R. A.Welch Foundation (F-1015). Instrumentation used in this work was developed and purchased through support from the NSF (IMR program) DMR-0216726 and from the Texas Coordinating Board (ATP-0099). Nanowires were fabricated using facilities of the Center for Nano and Molecular Science and Technology at UT Austin, supported in part by the R. A.Welch Foundation and by SPRING.