Filming the formation and fluctuation of skyrmion domains by cryo-Lorentz transmission electron microscopy
Edited by Margaret M. Murnane, University of Colorado at Boulder, Boulder, CO, and approved October 6, 2015 (received for review July 7, 2015)
Significance
The need for denser storage devices calls for new materials and nanostructures capable of confining single bits of information in a few nanometers. A new topological distribution of spins termed skyrmions is emerging, which promises to robustly confine a small magnetization in a few-nanometers-wide circular domain. A great deal of attention is being devoted to the understanding of these magnetic patterns and their manipulation. We manufactured a large nanoslice supporting over 70,000 skyrmions, and film their evolution in direct-space via cryo-Lorentz transmission electron microscopy. We reveal the octagonal distortion of the skyrmion lattice and show how these distortions and other defects impact its long-range order. These results pave the way to the control of a large two-dimensional array of skyrmions.
Abstract
Magnetic skyrmions are promising candidates as information carriers in logic or storage devices thanks to their robustness, guaranteed by the topological protection, and their nanometric size. Currently, little is known about the influence of parameters such as disorder, defects, or external stimuli on the long-range spatial distribution and temporal evolution of the skyrmion lattice. Here, using a large () single-crystal nanoslice (150 nm thick) of Cu2OSeO3, we image up to 70,000 skyrmions by means of cryo-Lorentz transmission electron microscopy as a function of the applied magnetic field. The emergence of the skyrmion lattice from the helimagnetic phase is monitored, revealing the existence of a glassy skyrmion phase at the phase transition field, where patches of an octagonally distorted skyrmion lattice are also discovered. In the skyrmion phase, dislocations are shown to cause the emergence and switching between domains with different lattice orientations, and the temporal fluctuation of these domains is filmed. These results demonstrate the importance of direct-space and real-time imaging of skyrmion domains for addressing both their long-range topology and stability.
Acknowledgments
We acknowledge Y. Tokura, F. Parmigiani, A. Rosch, C. Reichhardt, C. Olson-Reichhardt, and C. Hébert for useful discussions. Work at Laboratory for Ultrafast Microscopy and Electron Scattering was supported by European Research Council (ERC) Starting Grant USED258697 (to F.C.) and the National Center for Competence in Research Molecular Ultrafast Science and Technology (NCCR MUST), a research instrument of the Swiss National Science Foundation (SNSF). Work at Laboratory for Quantum Magnetism was supported by ERC project Controlled Quantum Effects and Spin Technology and SNSF (H.M.R.). The work of T.G. was supported in part by SNSF under Division II. The work of D.M. was supported by the Scottish Universities Physics Alliance.
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Published online: November 2, 2015
Published in issue: November 17, 2015
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Acknowledgments
We acknowledge Y. Tokura, F. Parmigiani, A. Rosch, C. Reichhardt, C. Olson-Reichhardt, and C. Hébert for useful discussions. Work at Laboratory for Ultrafast Microscopy and Electron Scattering was supported by European Research Council (ERC) Starting Grant USED258697 (to F.C.) and the National Center for Competence in Research Molecular Ultrafast Science and Technology (NCCR MUST), a research instrument of the Swiss National Science Foundation (SNSF). Work at Laboratory for Quantum Magnetism was supported by ERC project Controlled Quantum Effects and Spin Technology and SNSF (H.M.R.). The work of T.G. was supported in part by SNSF under Division II. The work of D.M. was supported by the Scottish Universities Physics Alliance.
Notes
This article is a PNAS Direct Submission.
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The authors declare no conflict of interest.
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Filming the formation and fluctuation of skyrmion domains by cryo-Lorentz transmission electron microscopy, Proc. Natl. Acad. Sci. U.S.A.
112 (46) 14212-14217,
https://doi.org/10.1073/pnas.1513343112
(2015).
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