Magnetostriction is a characteristic of ferromagnetic materials, such as Terfenol-D and Galfenol, which causes a change in shape in response to a magnetic field. This phenomenon is called the Joule Effect. During the application of a magnetic field the magnetic domains present in the material rotate to align with the field providing proportional, positive and repeatable expansion in microseconds.
Magnetostrictive materials can also convert mechanical work into electrical energy. Under the action of a mechanical load, magnetic domains rotate causing a bulk change in magnetization which can induce current in a coil. This behavior is commonly called the Villari Effect. Several applications exploit this reverse phenomenon of the material including vibration based energy harvesting devices and systems utilizing Galfenol.