Ferrofluid

Quick Answer: Ferrofluid is a liquid containing magnetic nanoparticles, usually iron oxide, coated with a surfactant and suspended in a carrier liquid. In a ferrofluid demonstration it is placed near a magnet, where it rises into spikes and follows the field, showing the shape of a magnetic field in three dimensions.

A Liquid That Responds to a Magnet

Each particle in ferrofluid is around ten nanometres across, far smaller than an iron filing, and a surfactant coating stops the particles clumping together. Random motion of the liquid keeps them suspended, so the fluid behaves as an ordinary liquid until a magnet comes near. Then every particle is pulled towards the stronger field, and the liquid as a whole moves and changes shape.

The most striking effect is the pattern of spikes that appears when a strong magnet is held underneath. Spikes form where the magnetic pull is balanced by the fluid’s surface tension and weight, and they line up along the field. Move the magnet and the spikes follow; take it away and the surface falls flat again, because the fluid is not permanently magnetised. A shallow glass Petri dish with the magnet held beneath it is a simple way to show this.

Ferrofluid therefore serves two lessons. In physics it makes magnetic fields visible in a way iron filings cannot, including in three dimensions. In chemistry it is an example of a colloid and of nanotechnology, where a surface coating decides whether particles stay dispersed. The same principle is used in some loudspeakers and rotary seals.

Applications

• Visualising the field around bar, horseshoe and disc magnets
• Explaining colloids, surfactants and nanoparticles in chemistry lessons
• Showing the difference between a permanently magnetised material and one that responds only while a field is present
• Open-day displays in a sealed cell or vial

Specifications

Care & Handling

• Keep ferrofluid in a closed container or sealed display cell; it stains skin, clothing, benches and paper, and the marks are hard to remove.
• Never let a magnet touch the fluid directly; the fluid coats the magnet and is very hard to clean off, so hold the magnet under a dish or behind glass.
• Wear gloves and eye protection when transferring it, and read the safety data sheet for the carrier liquid.
• Store the container upright and sealed, away from heat, to limit evaporation of the carrier.

Why Choose LabEquip

Physics and chemistry teachers looking for a memorable way to show magnetic fields or colloids buy ferrofluid in small quantities. LabEquip lists it under chemistry lab equipment; ask about volumes and display containers through the contact page.

Frequently Asked Questions

Is ferrofluid a magnet?

No. Ferrofluid has no permanent magnetism of its own. Its particles respond strongly to an external magnetic field, but when the magnet is removed, the fluid returns to an ordinary liquid shape.

Why does ferrofluid form spikes?

In a strong magnetic field the fluid is pulled along the field lines. Spikes form where that magnetic pull balances the fluid’s surface tension and weight, giving a regular pattern that follows the field.

Which container works well for demonstrations?

A shallow glass Petri dish or a sealed display cell works well. Place the magnet underneath rather than in the fluid, so the fluid can be seen reacting without coating the magnet.

How do I remove ferrofluid stains?

Stains are difficult to remove. For an oil-based fluid, blot with paper towel and then clean with a little detergent; on fabric, prevention is far easier than cleaning, so work over a tray lined with paper.

Why don’t the particles settle to the bottom?

They are so small that the random thermal motion of the liquid’s molecules keeps them suspended, and the surfactant coating stops them sticking together into larger clumps that would sink.

Is ferrofluid used outside the classroom?

Yes. Ferrofluids are used in some loudspeakers to cool and damp the voice coil, and in rotary seals that keep dust out of spinning shafts such as those in computer hard drives.

Last Updated: September 2026