Current-induced viscoelastic topological unwinding of metastable skyrmion strings

• Published in: Nature communications Vol. 8; no. 1; pp. 1332 - 8
• Main Authors: Kagawa, Fumitaka, Oike, Hiroshi, Koshibae, Wataru, Kikkawa, Akiko, Okamura, Yoshihiro, Taguchi, Yasujiro, Nagaosa, Naoto, Tokura, Yoshinori
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 06.11.2017; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/119/1001; 639/301/119/997; Computer simulation; Critical current density; Hall effect; Humanities and Social Sciences; multidisciplinary; Pulse duration; Science; Science (multidisciplinary); Strings; Unwinding; Viscoelasticity
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-017-01353-2

In the MnSi bulk chiral magnet, magnetic skyrmion strings of 17 nm in diameter appear in the form of a lattice, penetrating the sample thickness, 10–1000 μm. Although such a bundle of skyrmion strings may exhibit complex soft-matter-like dynamics when starting to move under the influence of a random pinning potential, the details remain highly elusive. Here, we show that a metastable skyrmion-string lattice is subject to topological unwinding under the application of pulsed currents of 3–5 × 10 6  A m –2 rather than being transported, as evidenced by measurements of the topological Hall effect. The critical current density above which the topological unwinding occurs is larger for a shorter pulse width, reminiscent of the viscoelastic characteristics accompanying the pinning-creep transition observed in domain-wall motion. Numerical simulations reveal that current-induced depinning of already segmented skyrmion strings initiates the topological unwinding. Thus, the skyrmion-string length is an element to consider when studying current-induced motion. Understanding the dynamics of the skyrmion string lattice is the prerequisite for its potential application as next-generation information carriers. Here, the authors explore the topological unwinding of skyrmion string lattice under the application of current pulses.