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

Area of Science:

• Physics
• Materials Science
• Colloidal Science

Background:

• Active matter systems exhibit complex behaviors influenced by external fields.
• Quincke electrorotational instability is a key mechanism for driving colloidal particle motion.
• Understanding particle dynamics under varying magnetic fields is crucial for designing new materials.

Purpose of the Study:

• To investigate the influence of magnetic fields on the motion of magnetite-doped colloidal spheres.
• To explore the emergence of distinct motion patterns in response to magnetic field strength.
• To elucidate the underlying physical mechanisms governing particle trajectories.

Main Methods:

• Experimental realization of an active matter system with motion restricted to four cardinal directions.
• Utilizing magnetite-doped colloidal spheres driven by Quincke electrorotational instability.
• Employing numerical simulations to analyze particle behavior and validate experimental findings.

Main Results:

• At zero magnetic field, particles exhibit circular trajectories with spontaneous runs.
• Intermediate magnetic fields (|B|≲20mT) linearize motion perpendicular to the field.
• High magnetic fields induce a second, distinct linearization parallel to the field.

Conclusions:

• Anisotropic magnetic susceptibility explains the observed linearization phenomena.
• The study reveals tunable directional motion in active matter systems.
• Findings offer insights into controlling colloidal dynamics for advanced applications.