Dynamics of domain formation in a ferromagnetic fluid

Abstract

Ferrofluids are colloidal suspensions of magnetic nanoparticles. Ferromagnetic ordering – with spontaneous net magnetization in the absence of external fields – has been described for a system of permanently magnetic nanoplatelets suspended in n-butanol, concentrated enough to undergo the transition to the nematic phase. Such material shows magnetic domain structures analogous to those of solid-state ferromagnets. Through optimization of fundamental interactions, the threshold concentration for nematic ordering was reduced. The optimized material allows reproducible and controllable analysis of domain structures and their formation dynamics, with domains forming on the time scale of the order of seconds. Finally, the effect of an external applied magnetic field on the nematic director fundamental fluctuations inside a domain has been studied with differential dynamic microscopy. Interestingly, the results provide an estimation of the ferrofluid's spontaneous magnetization in the absence of external magnetic fields.