VillariEffekt

The Villari effect refers to a magnetoelastic phenomenon in which mechanical stress alters the magnetic properties of a ferromagnetic material, most commonly its permeability and magnetization. The effect is observed when a stressed material is placed in a magnetic field, causing a stress-dependent change in magnetic response. It is part of the broader magnetoelastic family of effects that describe coupling between magnetic and elastic degrees of freedom in solids.

The underlying mechanism involves changes to magnetic anisotropy and domain structure caused by stress. When a ferromagnet is deformed, the energy landscape for magnetic moments shifts, leading to modifications in magnetization at a given external field. The strength of the Villari effect depends on the material’s magnetoelastic coupling and magnetostriction coefficients; larger coupling yields more pronounced changes in magnetic properties under stress.

Materials and magnitude vary widely. Soft ferromagnets such as iron alloys may exhibit relatively small but detectable changes in permeability under stress, while materials with strong magnetoelastic coupling, including certain nickel-iron or cobalt-based alloys, show more pronounced effects. Giant magnetostrictive materials like Terfenol-D (TbDyFe) or Galfenol demonstrate substantial coupling between magnetic fields, strain, and stress, making them especially suitable for sensor applications.

Applications of the Villari effect include stress and load sensing, structural health monitoring, and transducers for magnetoelastic sensors. In practice, devices exploit the stress-induced change in magnetic properties to detect mechanical changes or to convert magnetic energy into mechanical signals. The effect is closely related to magnetostriction, and together they describe the magnetoelastic coupling that links magnetic and elastic phenomena in materials.