Raphael Gruber1, Jakub Zázvorka2, Maarten A. Brems1, Davi R. Rodrigues1,3,4, Takaaki Dohi1, Nico Kerber1, Boris Seng1, Mehran Vafaee1, Karin Everschor-Sitte1,4, Peter Virnau1, Mathias Kläui1
1 Institute of Physics, Johannes Gutenberg-Universität Mainz, Staudingerweg 7, Mainz 55128, Germany
2 Institute of Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, Prague 12116, Czech Republic
3 Dipartimento di Ingegneria Elettrica e dell'Informazione, Politecnico di Bari, Via E. Orabona 4, Bari 70125, Italy
4 Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, Duisburg 47057, Germany
Magnetic skyrmions in thin films have been shown to exhibit thermal diffusion, making them a promising system for applications in probabilistic computing [1] as well as Brownian computing [2]. In such applications, pinning effects are of crucial importance as the pinning strength is often comparable to thermal excitations and thus impacts the operation of skyrmion-based devices. Using thermal skyrmion dynamics, we characterize the pinning in a sample and ascertain the spatially resolved energy landscape [3]. To understand the mechanism of pinning, we image the skyrmion pinning details and find a strong size-dependence. We observe that the skyrmion is pinned at its boundary (domain wall) and not as previously considered at its core. As a consequence, we find that the size-dependence follows from different favorable
overlaps of the skyrmion boundary with the pinning regions, which is supported by micromagnetic simulations and measurements of stripe domains (Fig. 1). This allows for dynamic switching of pinning sites and flexible tuning of the pinning.
Fig. 1. Left: Boundaries of skyrmions pinned at different positions. Right: Boundaries of stripe domains matching the skyrmion boundaries.
References
[1] J. Zázvorka et al., Nat. Nanotechnol. 14, 658 (2019).
[2] M. A. Brems, M. Kläui and P. Virnau, Appl. Phys. Lett. 119, 132405 (2021).
[3] R. Gruber et al., Nat. Commun. 13, 3144 (2022)