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

Eavan Fitzgerald; Cécile Clavaud; Debasish Das; Isaac C. D. Lenton; Scott R. Waitukaitis

doi:10.1103/1ss8-31rb

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

Eavan Fitzgerald, Cécile Clavaud, Debasish Das, Isaac C. D. Lenton, Scott R. Waitukaitis

Mathematics And Statistics

Research output: Contribution to journal › Article › peer-review

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 | ≲ 20 mT ) 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.

Original language	English
Article number	065418
Number of pages	8
Journal	Physical Review E
Volume	112
Issue number	6
DOIs	https://doi.org/10.1103/1ss8-31rb
Publication status	Published - 12 Dec 2025

Funding

This research was funded in whole or in part by the Austrian Science Fund (FWF) [Grant DOI: 10.55776/ESP298]. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 949120). This research was supported by the Scientific Service Units of The Institute of Science and Technology Austria (ISTA) through resources provided by the Miba Machine Shop, Nanofabrication Facility, Scientific Computing Facility, and Lab Support Facility. We wish to acknowledge the crucial contributions of Alexandre Morin in getting the project off the ground, and Jack Merrin for creating the SU-8 deposition protocol used in the construction of our cells. We also wish to thank Kimberley Modic and Hamza Nasir for their work on single-particle characterization.

Keywords

Living matter & active matter
Self-propelled particles

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Fitzgerald-etal-2025-Rolling-at-right-anglesFinal published version, 2.03 MBLicence: CC BY 4.0

Cite this

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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 | ≲ 20 mT ) 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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AU - Waitukaitis, Scott R.

PY - 2025/12/12

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AB - 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 | ≲ 20 mT ) 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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KW - Self-propelled particles

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JO - Physical Review E

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IS - 6

M1 - 065418

ER -

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

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