Deterministic creation and deletion of a single magnetic skyrmion observed by direct time-resolved X-ray microscopy

Abstract

Spintronic devices based on magnetic skyrmions are a promising candidate for next-generation memory applications due to their nanometre size, topologically protected stability and efficient current-driven dynamics. Since the recent discovery of room-temperature magnetic skyrmions, there have been reports of current-driven skyrmion displacement on magnetic tracks and demonstrations of current pulse-driven skyrmion generation. However, the controlled annihilation of a single skyrmion at room temperature has remained elusive. Here we demonstrate the deterministic writing and deleting of single isolated skyrmions at room temperature in ferrimagnetic GdFeCo films with a device-compatible stripline geometry. The process is driven by the application of current pulses, which induce spin–orbit torques, and is directly observed using a time-resolved nanoscale X-ray imaging technique. We provide a current pulse profile for the efficient and deterministic writing and deleting process. Using micromagnetic simulations, we also reveal the microscopic mechanism of the topological fluctuations that occur during this process.

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Fig. 1: Hysteresis behaviour of ferrimagnetic multilayer structure, and field- and current-driven domain evolution within the [Pt/GdFeCo/MgO]20 multilayer structure.
Fig. 2: Time-resolved pump–probe X-ray microscopy measurement.
Fig. 3: Micromagnetic simulation of the single skyrmion writing.
Fig. 4: Micromagnetic simulation of the single skyrmion deletion.

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Acknowledgements

This work was primarily supported by Samsung Research Funding Center of Samsung Electronics under project number SRFC-MA1602-01. Most experiments were performed at the MAXYMUS endstation at Berlin Electron Storage Ring Society for Synchrotron Radiation II (BESSYII), Helmholtz-Zentrum Berlin (HZB) (Berlin, Germany). Part of this work was performed at the PolLux (X07DA) endstation of the Swiss Light Source, Paul Scherrer Institut, Villigen, Switzerland. The authors acknowledge HZB for the allocation of beamtime. S.W., M.-C.P., K.-Y.L., J.W.C., B.-C.M., H.C.K. and J.C. acknowledge support from Korea Institute of Science and Technology (KIST) Institutional Program. K.M.S acknowledges support from the Sookmyung Women’s University BK21 Plus Scholarship. X.Z. was supported by Japan Society for the Promotion of Science (JSPS) RONPAKU (Dissertation PhD) Program. Y.Z. acknowledges support by the President’s Fund of The Chinese University of Shenzhen, Hong Kong (CUHKSZ), the National Natural Science Foundation of China (grant no. 11574137), and Shenzhen Fundamental Research Fund (grant nos. JCYJ20160331164412545 and JCYJ20170410171958839). M.E. acknowledges support by the Grants-in-Aid for Scientific Research from JSPS KAKENHI (grant nos. JP17K05490, 25400317 and 15H05854), and also support by Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology (JST) (grant no. JPMJCR16F1). J.W.C. acknowledges the travel fund supported by the National Research Foundation of Korea (NRF) funded by the The Ministry of Science, ICT and Future Planning (MSIP) of the Korea government (2016K1A3A7A09005418). S.W. and B.-C.M. acknowledge support from the National Research Council of Science and Technology (NST) grant (no. CAP-16-01-KIST) by MSIP.

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Contributions

S.W. designed and initiated the study. K.M.S. performed film growth, optimization and device fabrication on Si3N4 membranes. S.W., K.M.S. and J.W.C performed X-ray experiments with support from M.W. using STXM at BESSY2 in Berlin, Germany. X.Z., Y.Z. and X.L. performed the numerical simulations. M.E. carried out the theoretical analysis. During the revision of this Article, S.W., K.M.S., S.F. and J.R. performed X-ray imaging experiments as summarized in Supplementary Fig. 1 using STXM at Swiss Light Source in Villigen, Switzerland. M.-C.P. and K.-Y.L. provided technical support. S.W. and X.Z. drafted the manuscript and revised it with assistance from M.-C.P., K.-Y.L., J.W.C., B.-C.M., H.C.K. and J.C. All authors commented on the manuscript.

Corresponding author

Correspondence to Seonghoon Woo.

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Supplementary information

Supplementary Information

Supplementary Figures 1–9 and Supplementary Notes 1–3

Supplementary Video 1

Time-resolved STXM measurement showing the single skyrmion writing/deleting. The total length of the video in actual time is 2 μs and the time interval between two frames is 2 ns.

Supplementary Video 2

Time-resolved STXM measurement of skyrmion writing. This video is a part of the full dynamics shown in Supplementary Video 1, but the video speed is reduced so that the skyrmion configurations during the writing can be easily identified. The time-dependent current pulse evolution is simultaneously drawn to highlight pulse-dependent skyrmion changes.

Supplementary Video 3

Time-resolved STXM measurement of skyrmion deleting. This video is a part of the full dynamics shown in Supplementary Video 1, but the video speed is reduced so that the skyrmion configurations during the deleting can be easily identified. The time-dependent current pulse evolution is simultaneously drawn to highlight pulse-dependent skyrmion changes.

Supplementary Video 4

Simulated time-resolved spin configuration during the type-I writing pulse. A 400 × 400 nm2 square sample at B z  = 130 mT with relaxed ferrimagnetic spin ordering is used for the simulation. The central circle indicates the defect-like site, where the reduced PMA is applied. A strong pulse of j1 = −1.5 × 1012 A m–2 is applied for 200 ps, followed by a 200 ps-long weak pulse of j2 = +0.9 × 1012 A m−2 with the opposite polarity. The video frames show the top views of the whole simulated square sample where the boundary is indicated by a black line.

Supplementary Video 5

Simulated time-resolved spin configuration during the type-I writing pulse, where spin vectors are shown. This video is the same time-resolved dynamics of Supplementary Video 2, but in this video magnetic spins are represented as vectors so that the internal spin configuration changes within domain walls and around a vertical Bloch line (VBL) can be seen more effectively.

Supplementary Video 6

Simulated time-resolved spin configuration during the type-II writing pulse. A 400 × 400 nm2 square sample at B z  = 130 mT with relaxed ferrimagnetic spin ordering is used for the simulation. The central circle indicates the defect-like site, where the reduced PMA is applied. A strong pulse of j1 = –1.5 × 1012 A m−2 is applied for 200 ps, followed by a 200 ps-long weak pulse of j2 = –0.9×1012 A m−2 with the same polarity.

Supplementary Video 7

Simulated time-resolved spin configuration of a sample with three different defect-like sites during the type-I writing pulse. A 900 × 300 nm2 rectangular sample at B z  = 130 mT with relaxed ferrimagnetic spin ordering is used for simulations. The circles indicate the defect-like sites, where the reduced PMA is applied. In the left, middle, and right circles the minimum anisotropy is set as 0.2K u , 0.25K u , and 0.3K u , respectively (see Fig. 3b of the main text). A strong pulse of j1 = −1.5 × 1012 A m−2 is applied for 180 ps, followed by a 160 ps-long weak pulse of j2 = +0.9 × 1012 A m−2 with the opposite polarity.

Supplementary Video 8

Simulated time-resolved spin configuration during the deleting pulse: Case II of the main text. A 400 × 400 nm2 square sample at B z  = 130 mT and B x  = 70 mT with relaxed ferrimagnetic skyrmion texture is used for the simulation. A strong pulse of j = 1.6 × 1012 A m−2 and τ = 185 ps is applied.

Supplementary Video 9

Simulated time-resolved spin configuration during the deleting pulse: Case V of the main text. A 400 × 400 nm2 square sample at B z  = 130 mT and B x  = 70 mT with relaxed ferrimagnetic skyrmion texture is used for the simulation. A strong pulse of j = 2.2 × 1012 A m−2 and τ = 170 ps is applied.

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Woo, S., Song, K.M., Zhang, X. et al. Deterministic creation and deletion of a single magnetic skyrmion observed by direct time-resolved X-ray microscopy. Nat Electron 1, 288–296 (2018). https://doi.org/10.1038/s41928-018-0070-8

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