Delta E effect

The Delta E (ΔE) effect is a magnetomechanical effect. The name refers to changes in the effective elastic moduli of a magnetostrictive material, particularly the Young's modulus E, when a magnetic field is applied to a material.

This effect is connected to the tendency of a previously bent rod, made of magnetostrictive material, to straighten when subjected to a magnetic field applied along the rod's axis. This macroscopic effect is sometimes called the Guillemin effect, attributed to Claude-Marie Guillemin who first discussed the effect in 1846. The first explanations to the ΔE effect were given in the 1930s.

Description

The ΔE effect is often just considered in terms of a change of the effective Young modulus of a material under the application of a magnetic field. It is a consequence of the geometry and magnetic anisotropy of the magnetic domains. The Young's modulus changes from zero field to saturation. The change in theYoung's modulus ΔE is written as

$\Delta E=\frac{E_{\mathrm{s}}-E_0}{E_0},$

where

$E_{\mathrm{s}}$

is the Young modulus at saturation and

$E_0$

is the Young modulus in the unsaturated state. The effect is more general than this, and leads to changes in the values of all components of the elastic modulus tensor in a magnetic field.

Applications

The ΔE effect is used in applications to build actuators and sensors.

See also

• Magnetomechanical effects
• Magnetostriction
• Magnetocrystalline anisotropy