Abstract
Non-collinear and non-coplanar spin textures, such as chiral domain walls1 and helical or triangular spin structures2,3, bring about diverse functionalities. Among them, magnetic skyrmions, particle-like non-coplanar topological spin structures characterized by a non-zero integer topological charge called the skyrmion number (Nsk), have great potential for various spintronic applications, such as energy-saving, non-volatile memory and non-von Neumann devices4,5,6,7. Current pulses can initiate skyrmion creation in thin-film samples8,9,10 but require relatively large current densities, which probably causes Joule heating. Moreover, skyrmion creation is localized at a specific position in the film depending on the sample design. Here, we experimentally demonstrate an approach to skyrmion creation employing surface acoustic waves (SAWs); in asymmetric multilayers of Pt/Co/Ir, propagating SAWs induce skyrmions in a wide area of the magnetic film. Micromagnetic simulations reveal that inhomogeneous torque arising from both SAWs and thermal fluctuations creates magnetic textures, with pair structures consisting of a Néel skyrmion-like and an antiskyrmion-like structure. Subsequently, such pairs transform to a Néel skyrmion due to the instability of the antiskyrmion-like structure in a system with interfacial Dzyaloshinskii–Moriya interaction. Our findings provide a tool for efficient manipulation of topological spin objects without heat dissipation and over large areas, given that the propagation length of SAWs is of the order of millimetres.
This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
Data availability
The datasets generated and analysed during this study are available from the corresponding authors on reasonable request.
Code availability
The corresponding computer codes are available from the corresponding authors on reasonable request.
References
Emori, S., Bauer, U., Ahn, S.-M., Martinez, E. & Beach, G. S. D. Current-driven dynamics of chiral ferromagnetic domain walls. Nat. Mater. 12, 611–616 (2013).
Tokura, Y., Seki, S. & Nagaosa, N. Multiferroics of spin origin. Rep. Prog. Phys. 77, 076501 (2014).
Nakatsuji, S., Kiyohara, N. & Higo, T. Large anomalous Hall effect in a non-collinear antiferromagnet at room temperature. Nature 527, 212–215 (2015).
Fert, A., Cros, V. & Sampaio, J. Skyrmions on the track. Nat. Nanotechnol. 8, 152–156 (2013).
Nagaosa, N. & Tokura, Y. Topological properties and dynamics of magnetic skyrmions. Nat. Nanotechnol. 8, 899–911 (2013).
Zhang, X., Ezawa, M. & Zhou, Y. Magnetic skyrmion logic gates: conversion, duplication and merging of skyrmions. Sci. Rep. 5, 9400 (2015).
Zázvorka, J. et al. Thermal skyrmion diffusion used in a reshuffler device. Nat. Nanotechnol. 14, 658–661 (2019).
Jiang, W. et al. Blowing magnetic skyrmion bubbles. Science 349, 283–286 (2015).
Romming, N. et al. Writing and deleting single magnetic skyrmions. Science 341, 636–639 (2013).
Büttner, F. et al. Field-free deterministic ultrafast creation of magnetic skyrmions by spin-orbit torques. Nat. Nanotechnol. 12, 1040–1044 (2017).
Mühlbauer, S. et al. Skyrmion lattice in a chiral magnet. Science 323, 915–919 (2009).
Yu, X. Z. et al. Y. Real-space observation of a two-dimensional skyrmion crystal. Nature 465, 901–904 (2010).
Kézsmárki, I. et al. Néel-type skyrmion lattice with confined orientation in the polar magnetic semiconductor GaV4S8. Nat. Mater. 14, 1116–1122 (2015).
Boulle, O. et al. Room-temperature chiral magnetic skyrmions in ultrathin magnetic nanostructures. Nat. Nanotechnol. 11, 449–454 (2015).
Moreau-Luchaire, C. et al. Additive interfacial chiral interaction in multilayers for stabilization of small individual skyrmions at room temperature. Nat. Nanotechnol. 11, 444–448 (2016).
Woo, S. et al. Observation of room-temperature magnetic skyrmions and their current-driven dynamics in ultrathin metallic ferromagnets. Nat. Mater. 15, 501–506 (2016).
Nayak, A. K. et al. Magnetic antiskyrmions above room temperature in tetragonal Heusler materials. Nature 548, 561–566 (2017).
Chikazumi, S. Physics of Ferromagnetism 2nd edn, Ch.12 (Oxford Univ. Press, 1997).
Davis, S., Baruth, A. & Adenwalla, S. Magnetization dynamics triggered by surface acoustic waves. Appl. Phys. Lett. 97, 232507 (2010).
Weiler, M. et al. Elastically driven ferromagnetic resonance in nickel thin films. Phys. Rev. Lett. 106, 117601 (2011).
Weiler, M. et al. Spin pumping with coherent elastic waves. Phys. Rev. Lett. 108, 176601 (2012).
Foerster, M. et al. Direct imaging of delayed magneto-dynamic modes induced by surface acoustic waves. Nat. Commun. 8, 407 (2017).
Camara, I. S., Duquesne, J.-Y., Lemaître, A., Gourdon, C. & Thevenard, L. Field-free magnetization switching by an acoustic wave. Phys. Rev. Appl. 11, 014045 (2019).
Sugimoto, S., Kasai, S., Anokhin, E., Takahashi, Y. & Tokura, Y. Nonequilibrium skyrmion accumulation induced by direct current in Ir/Co/Pt heterostructure. App. Phys. Exp. 12, 073002 (2019).
Sugimoto, S. et al. Nonlocal accumulation, chemical potential, and Hall effect of skyrmions in Pt/Co/Ir heterostructure. Sci. Rep. 10, 1009 (2020).
Vansteenkiste, A. et al. The design and verification of MuMax3. AIP Adv. 4, 107133 (2014).
Tian, Z., Sander, D. & Kirschner, J. Nonlinear magnetoelastic coupling of epitaxial layers of Fe, Co, and Ni on Ir(100). Phys. Rev. B 79, 024432 (2009).
Viktorov, I. A. Rayleigh and Lamb Waves: Physical Theory and Applications Ch. 1 (Plenum, 1967).
Nepal, R., Güngördü, U. & Kovalev, A. A. Magnetic skyrmion bubble motion driven by surface acoustic waves. Appl. Phys. Lett. 112, 112404 (2018).
Deutsch, W. A. K., Cheng, A. & Achenbach, J. D. Self-focusing of Rayleigh waves and Lamb waves with a linear phased array. Res. Nondestruct. Eval. 9, 81–95 (1997).
Acknowledgements
We thank J. Puebla, K. Kondou and M. Xu for useful discussions. This work was supported by Scientific Research on Innovative Area ‘Nano Spin Conversion Science’ (grant no. 26103002), by the JSPS Grants-in-Aid for Scientific Research (A) (grant no. 18H03685) and for Young Scientists (19K14667) and by JST PRESTO (grant nos. JPMJPR18L3, JPMJPR18L5 and JPMJPR17I3).
Author information
Authors and Affiliations
Contributions
Y.O., S.K. and T.Y. conceived the project. S. Sugimoto and S.K. deposited the thin films. T.Y. fabricated the devices and conducted the measurements with assistance from B.R., S. Seki and N.O. T.Y. analysed the data and performed the simulation. T.Y. and Y.O. wrote the draft. All authors discussed the results and commented on the manuscript.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended data
Extended Data Fig. 1 Zoomed-out polar Kerr magnetic images.
Zoomed-out polar Kerr magnetic images before, during, and after exiting a surface acoustic wave (SAW) with the wavelength of 16 μm by applying RF signal with the power of 251 mW at 0.24 mT. The light blue dashed lines and the orange arrow represent the boundary of the Pt/Co/Ir film and propagating direction of the SAW, respectively. The orange dashed lines represents the area presented in Fig. 2a–c in the main text.
Extended Data Fig. 2 The effect of the wavelength on creation of skyrmions.
a, Magnetic field dependence of nsk before and after exciting a SAW with various wavelengths of SAW. b, The ratio of skyrmion density before and after exciting SAW with various wavelengths. The ratio for λSAW=16 μm is the largest among the four wavelengths as in the case of the difference of skyrmion density (Δnsk) (Fig. 3a in the main text), which further supports that the creation efficiency of skyrmions for the SAW with λSAW=16 μm is higher than that with λSAW=8 and 32 μm. The error bars correspond to the standard deviation.
Extended Data Fig. 3 Effect of the uniaxial strain.
a, A top view of the device. b-d, Polar Kerr magnetic images before and during applying constant voltage (± 18.8 V) at various magnetic fields.
Extended Data Fig. 4 Appearance process for inhomogeneous effective torque.
a-p Color maps of strain (εxx) (a-d), z-component of magnetization (e-h), x-component of magnetization (i-l), and effective torques resulting from the magnetoelastic coupling (m-p). The black circles exemplify the expansion of the area where effective torque is nonzero (see also the main text).
Extended Data Fig. 5 Micromagnetic simulations for skyrmion creations by surface acoustic waves.
a-f, Color maps of strain (εxx) (a), magnetization (b), topological charge density (ρtopo) (c), the sum of the exchange energy and Dzyaloshinskii-Moriya energy (Eex.+DM) (d), and effective torques resulting from the magnetoelastic coupling (e). The yellow squares denote the area presented in Fig. 4 in the main text.
Extended Data Fig. 6 Simulated wavelength dependences of the number and the size of skyrmions.
a, b, The wavelength dependences of the number of skyrmions (a) and the size of skyrmions (b). The broad blue line in (a) is guide to the eyes. c, A schematic for explaining the relationship between the wavelength and the length-scale of the effective torque.
Supplementary information
Supplementary Information
Supplementary Figs. 1–7 and discussion.
Supplementary Video 1
A movie representing the time evolution of the strain εxx, spin configurations, topological charge density, the sum of exchange and DMI energy density and effective torques arising from the magnetoelastic coupling in the whole process of the micromagnetic simulation.
Supplementary Video 2
Magnified version of movie S1, which represents the time evolution of the strain εxx, spin configurations, topological charge density, the sum of exchange and DMI energy density and effective torques arising from the magnetoelastic coupling to explicitly show the creation process of skyrmion.
Rights and permissions
About this article
Cite this article
Yokouchi, T., Sugimoto, S., Rana, B. et al. Creation of magnetic skyrmions by surface acoustic waves. Nat. Nanotechnol. 15, 361–366 (2020). https://doi.org/10.1038/s41565-020-0661-1
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41565-020-0661-1
