Chengkun Song1,2, Nico Kerber1, Jan Rothörl1, Yuqing Ge1, Klaus Raab1, Boris Seng1,3, Maarten A. Brems1, Florian Dittrich1, Robert M. Reeve1, Jianbo Wang2, Qingfang Liu2, Peter Virnau1, Mathias Kläui1
1 Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7, 55128 Mainz, Germany
2 Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000, P.R. China
3 Institute Jean Lamour, Université de Lorraine, Vandoeuvre-lès-Nancy 54506, France
Magnetic skyrmions are topological magnetic structures, which exhibit quasi-particle properties and can show enhanced stability against perturbation from thermal noise. Recently, thermal Brownian diffusion of these quasi-particles has been found in continuous films, and unconventional computing applications have received significant attention, requiring structured elements. Thus, as the next necessary step, skyrmion diffusion in confined geometries is studied, and it is found to be qualitatively different: The diffusion is governed by the interplay between the total number of skyrmions and the structure geometry. In particular, the effect of circular and triangular geometrical confinement is ascertained. It is found that for triangular geometries, the behavior is drastically different for the cases when the number of skyrmions in the element is either commensurate or incommensurate with a symmetric filling of the element (Fig. 1). This
influence of commensurability is corroborated by simulations of a quasi-particle model.
Fig. 1 Left: Average MOKE pictures of 5 and 6 skyrmions placed in a triangular structure. One can see the lattice ordering of 6 skyrmions compared to the less ordered structure of 5 skyrmions. Right: Mean-square-displacement of 1 to 10 skyrmions placed in this triangle. One sees a significantly reduced MSD for number commensurate with the triangle structure
References
[1] C. Song et al., Adv. Funct. Mater. 2010793, doi: 10.1002/adfm.202010739 (2021)