Temperature dependence of mechanical properties of the Fe₈₁Ga₁₉ (Galfenol) alloy

Mechanical properties of most metals or alloys are anelastic (i.e. not ideally Hookeian). The Fe₈₁Ga₁₉ (Galfenol) alloy is no exception. Mechanical properties, such as the Young's modulus (E) and damping capacity (▵W/W), were measured by the impulse excitation method under the following two conditions [1]: temperature (T) varied from room temperature (RT) to 300 °C, and [2] external magnetic field (H) changed from 0 to 200 Oe. In the E versus T plot (when H  =  0), there is a downward kink at T  =  T _mF  =  232 °C, which indicates that when T  <  T _mF, we have the un-relaxed Young's modulus (E _U), and when T  >  T _mF, the relaxed Young's modulus (E _R). The anelastic (or non-magnetic) ▵E effect (near T _mF) is defined as (▵E)_A  =  [E _U  −  E _R]/E _R  =  0.46% (a downward shift from E _U to E _R). In turn, in the E versus T plot (when H  =  200 Oe), there is almost no kink at T _mF, which implies an off-set due to the magnetic ▵E effect: (▵E)_H  =  [E _H  −  E _R]/E _R  =  2.67% (an upward shift from E _R to E _H), when T $\cong$ T _mF. The quality factor (1/Q) ≣ ([1/2][▵W/ W]) at constant flexure resonance frequency can be plotted as a function 1/T. From this plot, we conclude that (i) the experimental magnetic (or micro-eddy-current) damping capacity (mDC), due the magnetic domain wall (MDW) motion contribution, at Debye peak (i.e. when T  =  T _mF) is [▵W/ W]_eExp ≣ [▵W/ W]_H=200  −  [▵W/ W]_H=0  =  1.7%, while the theoretical mDC for the alloy is found to be [▵W/W]_eTh  =  1.2%; (ii) the activation energy, when H  =  200 Oe, is $\overline{E_A}$  =  0.81 eV atom⁻¹ (the Snoek type), and the activation energy, when H  =  0, is E _A  =  1.03 eV atom⁻¹. (paper)