Magneetstr

Magneetstr, short for magnetostrictive strain (often called magnetostriction in English), is the deformation that occurs in certain ferromagnetic materials when they are magnetized or exposed to a changing magnetic field. It is typically described by the fractional change in length ΔL/L along a given axis and by the magnetostriction coefficient λ in specific crystallographic directions. In static fields, magnetostriction can cause a material to elongate or contract up to parts per thousand or more, depending on composition and temperature.

Mechanism: The effect arises from magnetoelastic coupling between magnetic domain structure and the crystal lattice. Alignment of domains under a field can rotate, grow, or move domain walls, reducing magnetocrystalline anisotropy and causing lattice distortion. Anisotropy, crystallography, temperature, and mechanical constraints influence magnitude and sign.

Measurement: The coefficient λ defines maximum length change along the axis of magnetization at saturation. Dynamic magnetostriction is probed with alternating magnetic fields; strains are measured with strain gauges, laser Doppler vibrometry, or interferometry. Frequency response and hysteresis are important for device performance.

Materials and applications: Common magnetostrictive materials include Terfenol-D (TbDyFe) and Galfenol (Fe-Ga), which provide large strains and high coupling at room temperature. Applications include actuators, sensors, precision transducers, ultrasonic devices, and energy harvesting. Limitations include hysteresis, temperature dependence, mechanical fatigue, and relatively low efficiency at high frequencies for some alloys.

Terminology and history: The concept, called magnetostriction, was first observed in 1842 by James Joule. In some Dutch-language texts, magneetstr is used as an informal abbreviation for magnetostrictive strain.