Local structure in magnetostrictive melt-spun Fe80Ga20 alloys

We perform a detailed investigation of the local atomic structure in highly magnetostrictive alpha-FeGa melt-spun ribbons. By using extended x-ray absorption fine structure (EXAFS) analysis at the Fe and Ga K edges coupled to x-ray diffraction (XRD) and to ab initio, full multiple scattering calculations of the x-ray absorption near edge structure (XANES), we test for the presence of different local defect structures proposed in literature as being responsible for the large magnetostriction in these alloys. XRD shows that the ribbons crystallize in the A2 phase. Invisible by XRD, the presence of small Ga clusters is excluded by both EXAFS and XANES since no first shell Ga-Ga bonds are detected. However, EXAFS analysis of the second coordination shell around Ga clearly provides evidence for the presence of one highly strained (+4%) Ga-Ga pair and five Ga-Fe pairs, among the six crystallographically equivalent < 001 > atomic pairs. This conclusion supports recent total energy calculations that assign the large magnetostriction in these alloys to the strain caused by the rotation of the magnetization in the vicinity of such defects.