Magnetostrictive Materials

soft-magnetic materials that exhibit appreciable magnetostriction.

Magnetostrictive materials are used as converters of electromagnetic energy (for example, into mechanical energy), and for pressure transducers. Magnetostrictive materials include nickel and alloys such as Fe-Al (Alfer), Fe-Ni (Permalloy), Co-Ni, Fe-Co, and Co-Fe-V (Permendur); several ferrites (CoFe₂O₄ and NiFe₂O₄); and some rare earths and their alloys and compounds. Nickel has good magnetostrictive, mechanical, and anticorrosion properties. Permendur has large values of saturation magnetostriction Δ_s and magnetization. The ferrites have high specific electric resistivity and corrosion resistance; they are also the least expensive magnetostrictive materials.

Table 1 shows the initial and reversible magnetic permeability μ_a and μ_r, respectively, of magnetostrictive materials; the magnetostriction constant α = ((∂σ/∂β)_ε>), which characterizes the dependence of mechanical strain on the magnetic induction B of the specimen under conditions of constant deformation €; the sensitivity β = (∂β/∂σ)_h of magnetostrictive materials with respect to strain in a constant magnetic field H\\ and the coefficient of gyromagnetic coupling k, which is essential for magnetostrictive ultrasonic emitters (the ratio of the mechanical energy, which was converted by the emitter, to the electromagnetic energy supplied).

Table 1. Main characteristics of most important magnetostrictive materials
	Composition (% by mass)	μa	μr			k	λs × 106
Note: 1 dyne/(gauss-cm2) = 103 N/(T-m2); 1 (gauss-cm2)/dyne = 10-3 (T.m2)/ N
Nickel	999 Ni	200	50	16	61	0.30	35
Co-Ni	18 Co, 82 Ni	1,000	200	19	127	0.35	-25
Permendur	49 Co 2 V; remainder Fe	600	80	11	83	0.30	65
Iu14 (Alfer)	14 Al, 86 Fe	1,000	250	8	65	0.24	50
Ni-Co ferrite	NiO0.98Co0.02.Fe2O3	70	70	20	58	0.28	-25