Ferrofluid in a watchglass in the magnetic field produced by a neodymium magnet (not seen). The peaks formed in the ferrofluid are due to the magnetic field. Ferrofluids are colloidal liquids consisting of nanoscale ferromagnetic, or ferrimagnetic, particles (such as iron or an iron oxide) suspended in a fluid, usually an oil. Each tiny particle is thoroughly coated with a surfactant to inhibit clumping. One application of ferrofluids is to keep dust off the drive shafts of magnetic disk drives, which they do by creating a liquid seal held in place by magnetic fields.
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