Large-scale first-principles determination of anisotropic mechanical properties of magnetostrictive Fe-Ga alloys

Magnetostrictive Fe1−xGax alloys, as a new class of smart materials, have great potential in sensing and actuator applications. However, the fundamental understanding of the anisotropic elastic responses at high Ga concentration remains one of the most challenging problems for the binary alloys. Here, we apply the density functional theory and large-scale ab initio molecular dynamics simulation to investigate the effect of high Ga concentration on the elastic anisotropy of the Fe-Ga alloys with supercell models obtained by non-linear and non-uniform annealing processes. It is demonstrated that the formation of D03-like structures has an important effect on the softness of the tetragonal shear modulus and a negligible influence on the rhombohedral shear modulus. Meanwhile, the Fe dangling bond to its nearest Ga atoms results in a decrease in the Young's modulus and the negative Poisson's ratio in the [1 1 0] direction. The improved Young's modulus in the [1 1 0] direction compared to that in the [1 0 0] direction is attributed to the different arrangement of the pure Fe layer and the Fe-Ga mixed layer along the [1 1 0] and [1 0 0] axes. Furthermore, the ductility of Fe1−xGax alloys is enhanced at high Ga content, playing a key role in the enhanced magnetostriction.