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Rolling at right angles: Magnetic anisotropy enables dual-anisotropic active matter

Eavan Fitzgerald1, Cécile Clavaud1,2, Debasish Das3, Isaac C. D. Lenton1, and Scott R. Waitukaitis1,*

  • *Contact author: scott.waitukaitis@ist.ac.at
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Phys. Rev. E 112, 065418 – Published 12 December, 2025

DOI: https://doi.org/10.1103/1ss8-31rb

Abstract

We report on an experimental active matter system with motion restricted to four cardinal directions. Our particles are magnetite-doped colloidal spheres driven by the Quincke electrorotational instability. The absence of a magnetic field (|B|=0) leads to circular trajectories interspersed with short spontaneous runs. Intermediate fields (|B|≲20mT) linearize the motion along the axis perpendicular to B. At high magnetic fields, we observe the surprising emergence of a second, distinct linearization along the axis parallel to B. With numerical simulations, we show that this behavior can be explained by anisotropic magnetic susceptibility.

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Phys. Rev. E 112, 065418– Published 12 December, 2025
  • Received 24 July 2025
  • Accepted 12 November 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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