Both components of the tetragonal magnetoelastic constant b1: the saturation magnetostriction, λγ,2 = (3/2)λ100, and the magnetic-field saturated shear elasticity, c′ = (c11−c12)/2, were investigated over a wide temperature range for the magnetostrictiveFe1−x−yGaxGey alloys, (x+y ≅ 0.125, 0.185, and 0.245; x/y ≅ 1 and 3). The magnetostriction was measured from 77 to 425 K using standard strain gage techniques. Both shear elastic constants (c′ and c44) were measured from 5 to 300 K using resonant ultrasound spectroscopy. Six alloy compositions were prepared to cover three important regions: (I) the disordered solute α-Fe region, (II) a richer solute region containing both disordered and ordered phases, and (III) a rich solute region containing ordered multiphases. Our observations reveal that, when the data is presented versus the total electron/atom (e/a) ratio, the above regions for both the ternary and binary alloys are in almost perfect alignment. Following this analysis, we find that the magnetoelastic coupling, b1, peaks for both the binary and the ternary alloys at e/a ∼ 1.35. The values of c′ as well as of λγ,2 in region I of the ternary alloys, when plotted versus e/a, fall appropriately between the binary limits.
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