Crossover of microscopic dynamics in metallic supercooled liquid observed by NMR

Nuclear magnetic resonance is used to characterize local atomic motions in the glassy and supercooled liquid states of the bulk metallic glass system Pd43Ni10Cu27P20. The temperature dependence of the Knight shift reveals that certain local atomic motion decreases rapidly below a crossover temperature T-c down to the glass transition temperature T-g. Above T-c as well as below T-g the mean-squared amplitude of local motions depends linearly on the temperature. The observed gradual transition below T-c is inconsistent with heterogeneity effects. It reveals that qualitative changes of microscopic properties in the supercooled liquid take place at temperatures significantly above T-g.