Smart materials combine sensors, intelligence, and actuators to allow a material to respond to its environment. Magnetostrictive materials can be used as both the sensors and actuators in such materials. High-power magnetostrictive actuators can deliver forces greater than 50 MPa with strains of up to 0.6%, while other magnetostrictive sensor materials can provide hundreds of times the sensitivity of semiconductor strain gages. Magnetoelastic materials also have adaptable elastic moduli which may be varied by external magnetic fields.
Magnetostriction is the change in any dimension of a magnetic material caused by a change in its magnetic state. In this article we concentrate on ferromagnetic materials exhibiting Joule magnetostriction, which is a change in linear dimension parallel to an applied magnetic field (see Figure 1), and the reciprocal effect in which the material changes its magnetic state under the influence of applied stress.
The phenomenon of magnetostriction has been known for well over a century, since Joule discovered in 1847 the change in length of an iron rod when magnetized. The modern era of magnetostrictive materials began in 1963 with the measurement of nearly 1% magnetostrictive strains at low temperatures in the basal planes of Dy and Tb. A search for magnetostrictive materials with high magnetostriction at room temperature led to the alloying of rare earths with transition metals, culminating in the discovery in 1971 of giant room-temperature magnetostriction in the Laves phase compound TbFe2.