Magnetostriction

Summary

Magnetostriction is the change of shape or size of a ferromagnetic material when its magnetization changes. It comes from the coupling between the directions of the atomic magnetic moments and the crystal lattice. The strains are small, typically millionths, but some alloys such as Terfenol-D show a much larger effect. It causes the hum of transformers and is used in sonar transducers, actuators and sensors, together with its inverse, the change of magnetization under stress.