Induced Magnetic Anisotropy in Stress-Annealed Galfenol Alloys

Values of the uniaxial anisotropy, cubic anisotropy, saturation magnetic induction, and saturation magnetostriction were obtained from measurements of the magnetization and magnetostriction of stress-annealed Galfenol (Fe
_100-x
Ga
_x
,x=12.5,18.4, and 22.0)and Fe
₈₁
Al
₁₉
as a function of compressive stresses <100 MPa. The values were derived from fitting magnetization and magnetostriction curves to the energy expression E
_i
=-mu
₀
M
_s
Halpha
_z
+K
_cubic
(alpha
_x

⁴
+alpha
_y

⁴
+alpha
_z

⁴
)+K
_u
n
_iaxial
alpha
_z

²
-lambda
_sat
Talpha
_z

²
, where M
_s
,lambda
_sat
and the K's are fit parameters. The alpha
_i
's are the direction cosines of the magnetization direction with respect to the field and stress direction (z).H is the magnetic field and T is the measurement stress (compressive T<0). Data are fit with high precision by only the above four constants plus a smoothing constant. Importantly, K
_uniaxial
enables a prediction of the maximum usable tensile stress