arXiv subjects

Margaret Rosenberg

Publications and source records attributed to Margaret Rosenberg.

3 recordsLinked to original sources

arXiv2026

Magnetic active matter across scales

Magnetic interactions provide a versatile and powerful tool for controlling and organizing active matter, where individual units continuously consume energy to drive autonomous motion. These interactions arise naturally in biological systems, such as magnetotactic bacteria, and can be engineered into synthetic platforms, including colloidal microswimmers, magnetic nanoparticles, and macroscopic granular robots. This review focuses on active, self-propelled particles that carry an intrinsic magnetic dipole moment, powered by their own energy consumption rather than driven by external fields; here, the dipole moment mediates interactions and self-organization, not propulsion. We survey experimental and theoretical studies across all length scales, showing how dipolar interactions shape single-particle dynamics, collective behavior, and self-organization. We discuss models incorporating pairwise dipolar forces and confinement, and examine emergent phenomena such as chaining, swarming, and tunable pattern formation. We close by outlining challenges and opportunities in the design, control, and application of magnetic active systems, from programmable materials and biomedical actuation to nonequilibrium physics.

cond-mat.soft↗

arXiv2026

Windmilling clusters of active quadrupoles

Active matter has thrived in recent years, driven both by the insight that it underlies fundamental processes in nature, and by its vast potential for applications. This allows for innovation both inspired by experimental observations, and by construction of novel systems with desired properties. In this paper, we develop a novel system in the search for a new kind of pattern formation: microstructural motifs with orthogonal alignment. Taking a simple active Brownian particle (ABP) model applied to dumbbell-shaped particles, we add a quadrupolar interaction by positioning two antiparallel magnetic dipolar moments on each particle. We find that the phase behavior is determined by the competition between active motion and the orthogonal alignment favored by quadrupolar attraction. By varying these quantities, we are able to tune both the internal structure of the aggregates, and find a surprising stability of triangular aggregates, to the point of clusters of size $N=3$ being strongly overrepresented. Although none of the component particles are chiral, the resulting structures spin in a random, fixed direction due to combination of the polarity of the active motion. This results in an ensemble of windmilling (randomly spinning in a circular motion) aggregates with windmill-like shape (due to the three- or four core component dumbbells). Ultimately, this simple model shows an interesting range of microstructural motifs, with great potential for experimental implementations.

cond-mat.soft↗

arXiv2023

Role of ionic surfactant in magnetic dynamics of self-assembled dispersions of nanoplatelets

In complex colloidal systems, interparticle interactions strongly affect the dynamics of the constituting particles. A study of the dynamical response also provides invaluable information on the character of those interactions. Here we demonstrate how tuning the electrostatic interactions by an ionic surfactant in dispersions of magnetic nanoplatelets leads to developing new dynamic modes in magnetic response spectra. The collective modes can be induced or suppressed by either varying the concentration ratio of the magnetic nanoplatelets (MP) to the surfactant or increasing the MP concentration reflecting the nanoscale characteristics of this fluid magnet.

cond-mat.soft↗