Skyrmion Dynamics and a Resulting Spin Wave Fractal Network Probed with SANS*

Magnetic skyrmions present interesting and unique pseudo-particle behaviors which arise from their topological protection. Key among these behaviors is their microwave dynamic modes, which have potential as coupled spin torque oscillators with applications in on-chip wireless communications. Due to the small size and magnetic-only contrast of skyrmions, coupled with the high frequency of the dynamics – typically in the GHz regime – it is extremely challenging to perform in-situ measurements of these excitations. This work reports the use of small angle neutron scattering (SANS) to capture the dynamics in hybrid skyrmions. Using a static out-of-plane magnetic field and an in-plane microwave dynamic 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 the low-q scattering intensity in the form of a decay function which is absent in the off-resonant measurements. This scattering pattern is reasonably well fit with a Lorentzian model, representing spin wave excitation, however, a better fit is achieved using a mass fractal model, which suggests the spin waves form a long-range network-like structure. These results offer new insights into the nanoscale dynamics of magnetic skyrmions, but also present a unique use of SANS to probe high-speed dynamics.