Magnetostriction is a property of magnetic materials that causes them to change their shape or dimensions during the process of magnetization/Magnetic_Properties/Magnetostriction). When a magnetic field is applied to a magnetostrictive material, the material experiences a change in size or shape. The degree of magnetostriction can be measured by the magnetostrictive coefficient, which is the ratio of the fractional change in length or volume to the magnetization of the material/Magnetic_Properties/Magnetostriction).

Magnetostriction is a reversible effect, meaning that the material will return to its original shape and size when the magnetic field is removed/Magnetic_Properties/Magnetostriction). Magnetostrictive materials can convert magnetic energy into kinetic energy, or the reverse, and are used to build actuators and sensors.

There are several related effects to magnetostriction, including the Villari effect, the Matteucci effect, and the Wiedemann effect. The Villari effect is the change of the magnetic susceptibility of a material when subjected to a mechanical stress, while the Matteucci effect is the creation of a helical anisotropy of the susceptibility of a magnetostrictive material when subjected to a torque. The Wiedemann effect is the twisting of these materials when a helical magnetic field is applied to them.

Magnetostriction is commonly observed in ferromagnetic materials, which are materials that can be magnetized by an external field, and some ferrimagnetic materials, which are materials that have two opposite magnetic sublattices. The effect was first discovered by James Joule in 1842 when he observed that an iron rod elongated slightly when magnetized along its length, and contracted slightly when magnetized across its width.