Thermal stability of metastable magnetic skyrmions: entropic narrowing and significance of internal eigenmodes

Desplat, L., Suess, D., Kim, J.-V. and Stamps, R.L. (2018) Thermal stability of metastable magnetic skyrmions: entropic narrowing and significance of internal eigenmodes. Physical Review B, 98(13), 134407. (doi: 10.1103/PhysRevB.98.134407)

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We compute annihilation rates of metastable magnetic skyrmions using a form of Langer's theory in the intermediate-to-high damping (IHD) regime. For a Néel skyrmion, a Bloch skyrmion, and an antiskyrmion, we look at two possible paths to annihilation: collapse and escape through a boundary. We also study the effects of a curved versus a flat boundary, a second skyrmion, and a nonmagnetic defect. We find that the skyrmion's internal modes play a dominant role in the thermally activated transitions compared to the spin-wave excitations and that the relative contribution of internal modes depends on the nature of the transition process. Our calculations for a small skyrmion stabilized at zero field show that collapse on a defect is the most probable path. In the absence of a defect, the annihilation is largely dominated by escape mechanisms, even though in this case the activation energy is higher than that of collapse processes. Escape through a flat boundary is found more probable than through a curved boundary. The potential source of stability of metastable skyrmions is therefore found not to lie in high activation energies, nor in the dynamics at the transition state, but comes from entropic narrowing in the saddle point region which leads to lowered attempt frequencies. This narrowing effect is found to be primarily associated with the skyrmion's internal modes.

Item Type:Articles
Additional Information:This work was partially supported by the Horizon 2020 Framework Programme of the European Commission, under Grant agreement No. 665095 (MAGicSky). Additional support was received from CD-laboratory AMSEN (financed by the Austrian Federal Ministry of Economy, Family and Youth, the National Foundation for Research, Technology and Development), the FWF - SFB project F4112-N13. R. L. S. acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC).
Glasgow Author(s) Enlighten ID:Stamps, Professor Robert and Desplat, Louise
Authors: Desplat, L., Suess, D., Kim, J.-V., and Stamps, R.L.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Physical Review B
Publisher:American Physical Society
ISSN (Online):2469-9969
Published Online:04 October 2018
Copyright Holders:Copyright © 2018 American Physical Society
First Published:First published in Physical Review B 98(13):134407
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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