Magnetostriction is defined as “any change of the dimensions of an object caused by a change of its magnetic state”. Ferromagnetic materials have the strongest magnetostrictive effect which was demonstrated for the first time by Joules in 1842 (length change of the iron wire during the process of magnetization).

The Joules effect, concerning the change of the object caused by magnetization of a previously unmagnetized material, represents a direct magnetostrictive effect. In case of an already magnetized material there can be observed a change of the magnetic field in the object which exhibits changes of its mechanical characteristics, known as inverse magnetostrictive effect. The most familiar magnetostrictive effect is probably the Villari effect: Villari demonstrated that changes of the magnetic field in a ferromagnetic object occur under application of stress / force on the object.