Magnetostriction - Magnetostrictive Materials

Magnetostrictive Materials

Magnetostrictive materials can convert magnetic energy into kinetic energy, or the reverse, and are used to build actuators and sensors. The property can be quantified by the magnetostrictive coefficient, L, which is the fractional change in length as the magnetization of the material increases from zero to the saturation value. The effect is responsible for the familiar "electric hum" ( Listen) which can be heard near transformers and high power electrical devices (depending on country, either 100 (=2·50) or 120 (=2·60) hertz, plus harmonics).

Cobalt exhibits the largest room temperature magnetostriction of a pure element at 60 microstrains. Among alloys, the highest known magnetostriction is exhibited by Terfenol-D, (Ter for terbium, Fe for iron, NOL for Naval Ordnance Laboratory, and D for dysprosium). Terfenol-D, Tb_xDy_1-xFe₂, exhibits about 2,000 microstrains in a field of 2 kOe (160 kA/m) at room temperature and is the most commonly used engineering magnetostrictive material

Another very common magnetostrictive composite is the amorphous alloy Fe₈₁Si_3.5B_13.5C₂ with its trade name Metglas 2605SC. Favourable properties of this material are its high saturation magnetostriction constant, λ, of about 20 microstrains and more, coupled with a low magnetic anisotropy field strength, H_A, of less than 1 kA/m (to reach magnetic saturation). Metglas 2605SC also exhibits a very strong ΔE-effect with reductions in the effective Young's modulus up to about 80% in bulk. This helps build energy-efficient Magnetic MEMS .