A magnetic liquid is a substance containing in suspension particles of magnetic material with dimensions in the order of one-thousandth of a millimeter; sometimes it is also called ferrofluid. Characteristic of these liquids is the very high sensitivity to magnetic fields, this because each particle in suspension in the liquid has its magnetic moment, i.e., it behaves like a sort of micromagnet.
The main interests on magnetic liquids reside in their optical properties: for example, since the particles of magnetic liquid orient themselves in the presence of a magnetic field, it is possible to use magnetic fields to polarize these liquids properly and to ensure, from time to time, that they are transparent or opaque in light. This allows measuring the viscosity of the liquid and the presence of weak magnetic fields. In medicine, they are used in the localization of cancer cells and in the electronics industry where they are used for the realization of high-speed printers.