The effect concerning the change in the dimensions of a magnetic
substance caused by the external magnetic field.
The crystal lattices of a magnetic substance distort in a certain
direction even without any external magnetic field because the magnetic elements arranged in the
material distort the electrostatically connected arrangement by magnetic moment (magnetoelastic
energy). On the other hand, the elastic force of a substance counteracts, by the squared force, the
amount of distortion increased by the magnetic moment, reaching equilibrium at the minimum point of
the sum of both forces (elastic energy). If the dimensions of a ferromagnetic substance are finite,
the field is divided into smaller magnetic domains so that the sum of the spontaneous magnetization
direction is zero, thus minimizing the magnetostatic energy. The magnetization directions in a
domain are the same. If an external magnetic field is applied to the magnetic substance in a
certain direction, the direction of the magnetization inside each domain changes to that direction.
As a result, the dimension of the magnetic substance body changes by shifting from a state of the
crystal distortion with no external magnetic field to that with another point of equilibrium. This
effect can also be refered as magnetostrictive effect.