Tubular assemblies of magnetic particles act as microrobots for cargo transport [1]. The magnetization of such tubes comes in two families: Circular magnetization is preferred for short tubes, and axial magnetization for longer ones [2, 3]. Introducing the strength of the outer dipole ring as an order parameter [4] in a numerical simulation unveils the nature of that transition from circular to axial states [5]. [1] Xiaoyu Wang et al., PNAS 120, e2304685120 (2023). [2] Igor Stanković et al., Nanoscale 11, 2521 (2019). [3] Adrien Wafflard et al., New J. Phys. 25, 063024 (2023). [4] Simeon Völkel et al., JMMM 559, 169520 (2022). [5] Ingo Rehberg, Magnetic Tubes, Buckyballs, and other Drug Deliverers - Examine 537 dipole Clusters with a single Python Animation; DOI 10.5281/zenodo.10084573 (2023).

Talk presented at DPG Spring Meeting 2024: https://www.dpg-verhandlungen.de/year/2024/conference/berlin/part/dy/session/48/contribution/7?lang=en

In the experiment shown in the talk, the distance between two short tubes is actually used as a control parameter.

Text and slides are combined in a pdf. The movies are available in the previous version.