magnetostriction - Explanation, Magnetostrictive materials

The change in length of ferromagnetic materials when subject to a magnetic field. For example, nickel will contract along the field direction, and expand in the transverse direction. The effect results from the alignment of magnetic domains under the influence of the external field. It is exploited in ultrasonic transducers.

Magnetostriction (or the Joule effect) is a property of ferromagnetic materials that causes them to change their shape when subjected to a magnetic field. (Compare with electrostriction)

Explanation

Internally, ferromagnetic materials have a crystal structure that is divided into domains, each of which is a region of uniform magnetic polarisation. When a magnetic field is applied, the boundaries between the domains shift and the domains rotate, both these effects causing a change in the material's dimensions. Two other effects are related to magnetostriction: the Matteucci effect is the creation of a helical anisotropy of the susceptibility of a magnetostrictive material when subjected to a torque and the Wiedemann effect is the twisting of these materials when an helical magnetic field is applied to them.

Magnetostrictive materials

Magnetostrictive materials can convert magnetic energy into kinetic energy, or the reverse, and are used to build actuators and sensors. The property can be quantified by the magnetostrictive coefficient, L, which is the fractional change in length as the magnetization of the material increases from zero to the saturation value. Terfenol-D, TbxDy1-xFe2, exhibits about 2000 microstrains in a field of 2 kOe (160 kA/m) at room temperature and is the most commonly used engineering magnetostrictive material .