Magnetomechanical Coupling in Stress-Annealed Fe–Ga (Galfenol) Alloys

Magnetomechanical properties (coupling factor, piezomagnetic d-constant, and permeability) were obtained as a function of both magnetic field (0 to 600 Oe) and applied stress (-200 MPa to +50 MPa) for Fe_100-x Ga_x (x=12.5, 18.4, and 22). To evaluate the coupling factors Y^B, the Young´s modulus at constant induction, was measured and found to be 97, 75, and 67 GPa for x=12.5, 18.4, and 22, respectively. At low magnetic fields, relative permeabilities are greater than 800 for all alloys. Peak coupling factors exceeded 0.6 for the x=12.5 and x=18.4 alloys, whereas for the x=22 alloy, no measurable uniaxial energy was built into the alloy by stress annealing, and the d-constants and coupling factors were substantially lower. Model predictions of the inverse magnetostriction effect are presented for the x=18.4 alloy. Excellent fits obtained by the magnetization rotation model enable the calculation of all the magnetomechanical properties of the Fe-Ga system as well as the inverse magnetostrictive effect