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 (Delta W/W), were measured by the impulse excitation method under the following two conditions [1]: temperature (T) varied from room temperature (RT) to 300 degrees 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 degrees 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) Delta E effect (near T-mF) is defined as (Delta 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 Delta E effect: (Delta E)(H) = [E-H - E-R]/E-R = 2.67% (an upward shift from E-R to E-H), when T congruent to T-mF. The quality factor (1/Q). ([1/2][Delta 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 [Delta W/W](eExp) equivalent to [Delta W/W](H=200) -[Delta W/W] (H=0) = 1.7%, while the theoretical mDC for the alloy is found to be [Delta W/W](eTh) = 1.2%; (ii) the activation energy, when H = 200 Oe, is (E) over bar (A) = 0.81 eV atom(-1) (the Snoek type), and the activation energy, when H = 0, is E-A = 1.03 eV atom(-1).