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Skyrmion-Excited Spin-Wave Fractal Networks



Nan Tang, W. L. N. C. Liyanage, Sergio A. Montoya, Sheena Patel, Lizabeth J. Quigley, Alexander Grutter, Michael R. Fitzsimmons, Sunil Sinha, Julie A. Borchers, Eric E. Fullerton, Lisa Debeer-Schmitt, Dustin A. Gilbert


Magnetic skyrmions exhibit unique, technologically relevant pseudo-particle behaviors which arise from their topological protection, including well-defined, three-dimensional breathing and gyration modes which occur at microwave frequencies. During dynamic excitation, spin waves are ejected into the interstitial regions between skyrmions, which can interfere to create the magnetic equivalent of a choppy sea. However, since the spin waves generated in these systems have a well-defined length scale, and the skyrmions which generate them are on an ordered lattice, ordered structures from spin wave interference can precipitate from the chaos. This work uses small angle neutron scattering (SANS) to capture the dynamics in hybrid skyrmions and investigate the structure of the resulting spin waves. Using a static out-of-plane magnetic field and an in-plane microwave frequency excitation, driven gyration modes are generated in hybrid skyrmions. Coincident with the resonance conditions for the dynamics, the SANS pattern shows a large increase in low-q scattering intensity in the form of a decay function which is absent in the off-resonant measurements. This scattering pattern is reasonably represented by a Lorentzian model, indicative of spin wave excitation. However, a better fit is achieved using a mass fractal model, which suggests the spin waves form a long-range fractal network. The fractal structure is constructed of fundamental units which match the expected spin wave emissions and are constrained by the length scales of the skyrmion lattice. These results offer new insights into the nanoscale dynamics of magnetic skyrmions, identify a new dynamic spin wave fractal structure, and present a unique use of SANS to probe high-speed collective dynamics.
Advanced Materials


neutron scattering, magnetism, skyrmions, small angle scattering


Tang, N. , Liyanage, W. , Montoya, S. , Patel, S. , Quigley, L. , Grutter, A. , Fitzsimmons, M. , Sinha, S. , Borchers, J. , Fullerton, E. , Debeer-Schmitt, L. and Gilbert, D. (2023), Skyrmion-Excited Spin-Wave Fractal Networks, Advanced Materials, [online], (Accessed June 23, 2024)


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Created August 18, 2023, Updated January 23, 2024