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

TL;DR

This paper introduces an active matter system where particles move in four directions, with magnetic anisotropy enabling control of their motion, revealing novel dual-direction linearization phenomena.

Contribution

The study demonstrates how magnetic anisotropy can induce dual-direction linearization in active particles, a novel control mechanism for active matter systems.

Findings

Particles exhibit directional motion restricted to four axes.

Magnetic fields induce linearization of trajectories along specific axes.

Numerical simulations explain behavior via anisotropic magnetic susceptibility.

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