Dresden 2017 – scientific programme

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BP: Fachverband Biologische Physik

BP 41: Active Matter I (Joint Session DY/BP/CPP)

BP 41.1: Talk

Wednesday, March 22, 2017, 15:00–15:15, HÜL 186

Flocking ferromagnetic particles — •Andreas Kaiser, Alexey Snezhko, and Igor S. Aranson — Materials Science Division, Argonne National Laboratory, 9700 South Cass Ave, Argonne, Illinois 60439, USA

Suspensions of microswimmers, show fascinating collective behaviours like clustering, flocking and turbulence [1]. Here, we demonstrate the discovery of ferromagnetic flocking colloids. The self-propulsion is an outcome of the spontaneous rotation of a ferromagnetic colloidal sphere in a vertical alternating (AC) magnetic field [2]. Depending on the frequency of this magnetic field, a sequence of transitions can be observed: from gas-like motion of individual particles to the onset of flocking and global rotation followed by a reentrant flocking and gas-like state for increasing frequency [3]. We also emphasize a subtle role of rotational noise: While the low-frequency flocking appears to be noise-insensitive, the reentrant flocking happens to be noise-activated. Moreover, we uncover a new relation between collective motion and synchronisation.

[1] T. Vicsek, A. Zafeiris, Physics Reports 517, 71 (2012)

[2] G. Kokot, D. Piet, G.M. Whitesides, I.S. Aranson, A. Snezkho, Scientific Reports 5, 9528 (2015)

[3] A. Kaiser, A. Snezkho, I.S. Aranson, Science Advances (submitted)