Fluctuation and dynamics of magnetic skyrmions*

Recently discovered skyrmions is an example of a topological phase that manifest in magnetic systems as a hexagonal lattice of spin vortices. Understanding driven dynamics and spontaneous fluctuations of the skyrmions is fundamentally important to determine the robustness of the topological particles which is an important factor to consider for their use in magnetic logic and storage applications. We have shown that resonant x-ray scattering is a powerful tool to study skyrmion [1,2]. We will report on ultrafast x-ray scattering studies on skyrmion material Cu2OSeO3 using laser pump-x-ray probe. The excitation of the skyrmion phase shows a nonlinear dependence on the excitation density, in contrast to the excitation of the conical phase which is linearly dependent on the excitation density [3]. We will also discuss a new experimental technique that uses a time-delayed femtosecond x-ray pulse pair to perform correlation spectroscopy at nanosecond time scales to study fluctuations on Fe-Gd thin film samples that exhibit stripe and skyrmion phase [4]. When the applied field was tuned for skyrmions in the sample, the fluctuations were found to de-correlate within a period of about 4 nanoseconds. At the stripe-skyrmion phase boundary, the fluctuation period decreased to only a fraction of a nanosecond indicative of enhanced fluctuation at the stripe-skyrmion phase boundary.

[1]. M. C. Langner, S. Roy et al., Phys. Rev. Lett. 112, 167202 (2014).
[2]. J. C. T Lee et al, Appl. Phys. Lett. 109, 022402 (2016).
[3]. M. C. Langner, S. Roy et al, Phys. Rev. Lett. 119, 107204 (2017)
[4]. M. H. Seaberg et. al., Phys. Rev. Lett, 119, 067403 (2017).