Neodymium iron-boron rare-earth magnet

Ferrofluids are colloidal mixtures - where one substance is microscopically dispersed evenly throughout a carrier fluid - containing magnetic nanoparticles.

When placed in a magnetic field, the suspended particles cause the entire fluid to become strongly magnetised.

In this image a small drop of ferrofluid is placed within a magnetic field created by a neodymium iron-boron rare-earth magnet. The peaks and troughs result as the magnet tries to pull the liquid along its field lines.

Ferrofluids are being used in experimental cancer treatments called magnetic hyperthermia, and are the basis for a new breed of shape-shifting telescope lenses.