Structural and dynamical changes in a Gd-Co metallic glass by cryogenic rejuvenation

To experimentally clarify the changes in structural and dynamic heterogeneities in a metallic glass (MG), Gd65Co35, by rejuvenation with temperature cycling (cryogenic rejuvenation), high-energy X-ray diffraction (HEXRD), anomalous x-ray scattering (AXS), and inelastic x-ray scattering (IXS) experiments were carried out. By repeated temperature changes between liquid N2 and room temperatures 40 times, we observed tiny but clear structural changes by HEXRD even in the first-nearest neighbor range. The partial structural information obtained by AXS revealed that slight movements of Gd and Co atoms occur in the first- and second-nearest neighbor shells around the central Gd atom. The composition heterogeneity in nanometer size is markedly increased for the Gd atoms by temperature cycling, whereas the other heterogeneities are negligible. A distinct change was detected in microscopic elastic property by IXS: The width of longitudinal acoustic excitation broadens by about 20%, indicating an increase in the elastic heterogeneity of this MG induced by thermal treatments. These static and dynamic results explicitly clarify the features of the cryogenic rejuvenation effect experimentally.