A colloidal suspension of Fe3O4 nanoparticles acts as a magnetic "liquid" and forms amazing spikes when a magnet is brought close. The particles act as small compasses marking the magnetic field lines of the magnet.

The ferrofluid you see consists of magnetic nanoparticles suspended in water. As a magnet is brought up to the ferrofluid, spikes form in the fluid and can dance in response to movements of the magnet.
Synthesis of aqueous ferrofluid.

Oil-based commercial ferrofluid is poured into a dish.

Magnets are lowered close to the ferrofluid, and then raised.

Magnets are lowered close to the ferrofluid, and then raised. The ferrofluid follows the magnetic field lines.

Ferrofluid attracted to a magnet has an apparent density that is large enough to displace a penny. (This technique can be used for separations. See American Mineralogist, 62, 374-376 (1977).)

A lever raises and lowers a cow magnet between two bottle cells containing water and ferrofluid. (Part of the MRSEC Nanoworld Display.)

A knob turns an array of magnets and ferrofluid in bottle cells respond. (Part of the MRSEC Nanoworld Display.)

Exploring the Nanoworld | MRSEC Nanostructured Interfaces
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This page created by George Lisensky, Beloit College.  Last modified July 2, 2011 .