Ramin Golestanian1 Fanlong Meng1 Daiki Matsunaga1

1, University of Oxford , Oxford, , United Kingdom

Magnetic active matter constitutes a particularly interesting class of systems, not least because of its versatility in terms of the fabrication of artificial swimmers and their control, as well as its potential for technological applications. We investigate the collective behavior of magnetic swimmers, which are suspended in a Poiseuille flow and placed under an external magnetic field, using analytical techniques and Brownian dynamics simulations. We find that the interplay between intrinsic activity, external alignment, and magnetic dipole-dipole interactions leads to longitudinal structure formation. Our work sheds light on a recent experimental observation of a clustering instability in this system.