Raphael Gruber, Tobias Sparmann, Maarten A. Brems, Jan Rothörl, Peter Virnau, Mathias Kläui
Institute of Physics, Johannes Gutenberg University Mainz
Magnetic skyrmions, topological spin textures appearing as quasi-particles, are considered promising candidates for the implementation of probabilistic computing devices since they respond strongly nonlinear to external stimuli and feature inherent multiscale dynamics [1].
The implementation of such reservoir computing relies on thermal excitation of the magnetic skyrmions within thin films exhibiting pinning due to sample defects [2]. The combination of skyrmion diffusion and current-induced motion has been shown to be useful in Brownian reservoir computing devices [3] and other probabilistic computing applications. As large sample-specific defects create spatial bias in such systems, a depinning procedure is needed for a space-independent motion. To reach a regime of near free diffusion, we propose and experimentally demonstrate depinning applying alternating electric and magnetic fields to the sample. In particular, we show that the energy landscape is effectively flattened and diffusion is drastically enhanced for sufficient excitation. This effect can therefore be useful to reduce pinning effects and thus accelerate non-conventional computing devices as well as to lower thresholds for current-induced skyrmion motion due to smaller pinning effects.
Fig.1. Skyrmion diffusion coefficient D in dependence of magnetic field oscillation frequency and amplitude.
References
[1] D. Prychynenko, M. Sitte, et al., Physical Review Applied, vol. 9, no. 1, 31, 2018.
[2] R. Gruber, J. Zazvorka, et al., Nature Communications, vol. 13, no. 1, 6, 2022.
[3] J. Zazvorka, F. Jakobs, et al., Nature Nanotechnology, vol. 14, no. 7, 2019.