The giant magnetostriction observed in rare-earth transition-metal compounds such as Terfenol-D (Tb0.3Dy0.7Fe2) is commonly associated with the huge anisotropy of the 4f electron cloud. We report here the experimental observation of this phenomenon at the atomic scale, in amorphous matter. By using extended x-ray absorption fine structure spectroscopy in a differential mode, the bond strains resulting from the coupling between the anisotropic shape of the Tb 4f charge density and the environment crystalline electric field are measured. In a-TbFe2 we measure Fe-Fe and Fe-Tb bond contractions equal to 6(1)x 10−4 Å and of 9(2) x 10−4 Å, respectively. These are the smallest atomic displacements ever detected in amorphous matter.
4f charge-density deformation and magnetostrictive bond strain observed in amorphous TbFe2 by x-ray absorption spectroscopy / Pascarelli, S.; Ruffoni, M. P.; Trapananti, A.; Mathon, O.; Detlefs, C.; Pasquale, Massimo; Magni, Alessandro; Sasso, CARLO PAOLO; Celegato, F.; Olivetti, ELENA SONIA; Joly, Y.; Givord, AND D.. - In: PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS. - ISSN 1098-0121. - 81:(2010), pp. 020406-1-020406-4. [10.1103/PhysRevB.81.020406]