Skyrmion lattice formation and destruction mechanisms probed with TR-SANS

W. L. N. C. Liyanage; Nan Tang; Rebecca L. Dally; Lizabeth J. Quigley; C. Charlotte Buchanan; Guo-Jiun Shu; Nicholas P. Butch; Kathryn Krycka; Markus Bleuel; Julie A. Borchers; Lisa Debeer-Schmitt; Dustin A. Gilbert

doi:10.1039/D4NR00858H

Skyrmion lattice formation and destruction mechanisms probed with TR-SANS

W. L. N. C. Liyanage,^a Nan Tang,

^b Rebecca L. Dally,

^c Lizabeth J. Quigley,

^b C. Charlotte Buchanan,^b Guo-Jiun Shu,

^de Nicholas P. Butch,

^cf Kathryn Krycka,^c Markus Bleuel,

^cg Julie A. Borchers,

^c Lisa Debeer-Schmitt

^h and Dustin A. Gilbert

*^ab

Author affiliations

* Corresponding authors

^a Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA
E-mail: dagilbert@utk.edu

^b Materials Science Department, University of Tennessee, Knoxville, TN 37996, USA

^c NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA

^d Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan

^e Department of Materials and Mineral Resources Engineering, Institute of Mineral Resources Engineering, National Taipei University of Technology, Taipei 10608, Taiwan

^f Center for Nanophysics and Advanced Materials, Department of Physics, University of Maryland, College Park, MD 20742, USA

^g Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, USA

^h High Flux Isotope Reactor, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA

Abstract

Magnetic skyrmions are topologically protected, nanoscale whirls of the spin configuration that tend to form hexagonally ordered arrays. As a topologically non-trivial structure, the nucleation and annihilation of the skyrmion, as well as the interaction between skyrmions, varies from conventional magnetic systems. Recent works have suggested that the ordering kinetics in these materials occur over millisecond or longer timescales, which is unusually slow for magnetic dynamics. The current work investigates the skyrmion ordering kinetics, particularly during lattice formation and destruction, using time-resolved small angle neutron scattering (TR-SANS). Evaluating the time-resolved structure and intensity of the neutron diffraction pattern reveals the evolving real-space structure of the skyrmion lattice and the timeframe of the formation. Measurements were performed on three prototypical skyrmion materials: MnSi, (Fe,Co)Si, and Cu₂OSeO₃. To probe lattice formation and destruction kinetics, the systems were prepared in the stable skyrmion state, and then a square-wave magnetic field modulation was applied. The measurements show that the skyrmions quickly form ordered domains, with a significant distribution in lattice parameters, which then converge to the final structure; the results confirm the slow kinetics, with formation times between 10 ms and 99 ms. Comparisons are made between the measured formation times and the fundamental material properties, suggesting the ordering temperature, saturation magnetization and magnetocrystalline anisotropy may be driving the timeframes. Micromagnetic simulations were also performed and support a scaling of the kinetics with sample volume, a behavior which is caused by the reconciling of misaligned domains.

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Skyrmion lattice formation and destruction mechanisms probed with TR-SANS

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Skyrmion lattice formation and destruction mechanisms probed with TR-SANS

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