Using differential x-ray absorption spectroscopy (DiffXAS) we have measured and quantified the intrinsic, atomic-scale magnetostriction of ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$. By exploiting the chemical selectivity of DiffXAS, the Fe and Ga local environments have been assessed individually. The enhanced magnetostriction induced by the addition of Ga to Fe was found to originate from the Ga environment, where ${\lambda }^{\gamma ,2}(\approx (3/2){\lambda }_{100})$ is $390\pm 40\mathrm{ppm}$. In this environment, $⟨001⟩$ Ga-Ga pair defects were found to exist, which mediate the magnetostriction by inducing large strains in the surrounding Ga-Fe bonds. For the first time, intrinsic, chemically selective magnetostrictive strain has been measured and quantified at the atomic level, allowing true comparison with theory.

The effect of the volume expansion on the total linear magnetostriction of ${\mathrm{Fe}}_{85}{\mathrm{Ga}}_{15}$ , ${\mathrm{Fe}}_{80}{\mathrm{Ga}}_{20}$ , and ${\mathrm{Fe}}_{71}{\mathrm{Ga}}_{29}$ mold-cast bulk alloys was investigated by measuring the change in length with applied field longitudinal and perpendicular to the temperature gradient during solidification. In the magnetically saturated state, due to the contribution of the volume expansion, the saturation magnetostriction for all three alloys was about 66 % of the total linear magnetostriction. The magnetostriction is strongly dependent on the direction of the temperature gradient, being larger in this direction. The substitution of Fe by Ga atoms increases the lattice constant and causes a change to the $A2$ crystal structure, which was confirmed by Mössbauer spectroscopy. The thermal-expansion coefficient increases with Ga content at temperatures between 4.2 and $150\mathrm{K}$ .