Local structural changes in a Gd 65 Cu 35 metallic glass by cryogenic rejuvenation: comparison with other Gd transition metal alloys

As a part of a systematic study on the structural changes of Gd-transition metal (TM) alloy glasses induced by cryogenic rejuvenation, high-energy X-ray diffraction (HEXRD) and anomalous X-ray scattering (AXS) measurements were performed on a Gd$_{65}$Cu$_{35}$ metallic glass (MG) possessing minimal elastic heterogeneity, as indicated by dynamical mechanical analysis. Significant structural changes {were observed in} this MG as a result of temperature {cyclings} between liquid N$_2$ and room temperatures 40 times. 1) HEXRD revealed {minor} changes {in} the first nearest neighbour range of the pair distribution function, $g(r)$, {consistent with observations} in other Gd$_{65}$TM$_{35}$ glasses. 2) The partial structural information obtained from HEXRD and AXS showed that Gd-Cu and Cu-Cu partial correlations dominate the first peak region of the total $g(r)$, whereas Gd-Gd correlations contribute mainly to the second peak. 3) {Additionally,} some of the Gd-Cu and Cu-Cu correlations extend to the second peak of the total $g(r)$, unlike {in} Gd$_{65}$Co$_{35}$ and Gd$_{65}$Ni$_{35}$ MGs. 4) {Futhermore,} Cu atoms shift farther from each other by cryogenic rejuvenation. 5) Heterogeneities {in} the Cu elemental composition and the total number density {at nm length scale} increase by cryogenic rejuvenation, similar to the Gd$_{65}$Co$_{35}$ MG but opposite to {the trend observed} in the Gd$_{65}$Ni$_{35}$ MG. Accordingly, {these findings suggest} that structural heterogeneity in MGs {is} not systematically related to the extent of elastic heterogeneity.