Abstract
Magnetic skyrmions are promising candidates for future spintronic applications such as skyrmion racetrack memories and logic devices. They exhibit exotic and complex dynamics governed by topology and are less influenced by defects, such as edge roughness, than conventionally used domain walls. In particular, their non-zero topological charge leads to a predicted ‘skyrmion Hall effect’, in which current-driven skyrmions acquire a transverse velocity component analogous to charged particles in the conventional Hall effect. Here, we use nanoscale pump–probe imaging to reveal the real-time dynamics of skyrmions driven by current-induced spin–orbit torques. We find that skyrmions move at a well-defined angle ΘSkH that can exceed 30° with respect to the current flow, but in contrast to conventional theoretical expectations, ΘSkH increases linearly with velocity up to at least 100 ms−1. We qualitatively explain our observation based on internal mode excitations in combination with a field-like spin–orbit torque, showing that one must go beyond the usual rigid skyrmion description to understand the dynamics.
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Acknowledgements
Work at MIT was primarily supported by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under Award #DE-SC0012371 (sample fabrication). G.S.D.B. acknowledges support from C-SPIN, one of the six SRC STARnet Centers, sponsored by MARCO and DARPA. M.K. and the group at Mainz acknowledge support by the DFG (in particular SFB TRR173 Spin + X), the Graduate School of Excellence Materials Science in Mainz (MAINZ, GSC 266), the EU (MultiRev (ERC-2014-PoC 665672), MASPIC (ERC-2007-StG 208162), WALL (FP7-PEOPLE-2013-ITN 608031)), SpinNet, a topical network project of the German Academic Exchange Service (DAAD), and the Research Center of Innovative and Emerging Materials at Johannes Gutenberg University (CINEMA). M.K. thanks ICC-IMR at Tohoku University for their hospitality during a visiting researcher stay at the Institute for Materials Research. B.K. is grateful for financial support by the Carl-Zeiss-Foundation. F.B. acknowledges financial support by the German Research Foundation through grant no. BU 3297/1-1. O.A.T. acknowledges support by the Grants-in-Aid for Scientific Research (Grants No. 25800184, No. 25247056, and No. 15H01009) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan and SpinNet. K.L. gratefully acknowledges financial support by the Graduate School of Excellence Materials Science in Mainz (MAINZ) and the help and advice of Karin Everschor-Sitte and technicians of the Kläui group, especially S. Kauschke. Measurements were carried out at the MAXYMUS end station at Helmholtz-Zentrum Berlin. We thank HZB for the allocation of beamtime. Parts of this research were conducted using the supercomputer Mogon offered by Johannes Gutenberg University Mainz (hpc.uni-mainz.de), which is a member of the AHRP and the Gauss Alliance e.V.
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M.K. and G.S.D.B. proposed and supervised the study. I.L. and K.L. fabricated devices. I.L. performed the film characterization. K.L., L.C., K.R., P.B., J.F., R.M.R., H.S., G.S., I.B. and M.W. conducted STXM experiments on the MAXYMUS beamline at the BESSY II synchrotron in Berlin. K.L. and M.K. performed and analysed the micromagnetic simulations. B.K., K.S. and O.A.T. derived a Thiele equation to explain the micromagnetic simulations and provided input for the latter. K.L., P.B. and K.R. performed the analytical analysis of the experimental data. F.B. derived the expression for the skyrmion Hall angle as a function of the domain wall width. All authors participated in the discussion and interpreted results. K.L. drafted the manuscript with the help of M.K. and assistance from G.S.D.B. All authors commented on the manuscript.
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Litzius, K., Lemesh, I., Krüger, B. et al. Skyrmion Hall effect revealed by direct time-resolved X-ray microscopy. Nature Phys 13, 170–175 (2017). https://doi.org/10.1038/nphys4000
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DOI: https://doi.org/10.1038/nphys4000
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