Villari Effect

the effect of mechanical deformation (stretching, twisting, and bending) on the magnetization of a ferromagnetic.

Discovered in 1865 by the Italian physicist E. Villari (1836-1904), the effect is the opposite of magnetostriction— change in the size of a ferromagnetic during magnetization. Ferromagnetics (nickel, for example) that shrink during magnetization (have negative magnetostriction) lose some of their magnetic qualities when stretched (negative Villari effect). On the other hand, the stretching of ferromagnetics with positive magnetostriction (for example, a bar of iron-nickel alloy with 65 percent nickel) leads to an increase in their magnetic properties (positive Villari effect). During compression the sign of the Villari effect switches to its opposite. The Villari effect is explained by the fact that the domain structure of a ferromagnetic, which determines its magnetic properties, changes when mechanical force is applied. It is used in creating materials with given magnetic properties.