  Understanding and controlling physical aging, i.e. the spontaneous temporal
evolution of out-of-equilibrium systems, represents one of the greatest tasks
in material science. Recent studies have revealed the existence of a complex
atomic motion in metallic glasses, with different aging regimes in contrast
with the typical continuous aging observed in macroscopic quantities. By
combining dynamical and structural synchrotron techniques, for the first time
we directly connect previously identified microscopic structural mechanisms
with the peculiar atomic motion, providing a broader unique view of their
complexity. We show that the atomic scale is dominated by the interplay between
two processes: rearrangements releasing residual stresses related to a cascade
mechanism of relaxation, and medium range ordering processes, which do not
affect the local density, likely due to localized relaxations of liquid-like
regions. As temperature increases, a surprising additional secondary relaxation
process sets in, together with a faster medium range ordering, likely
precursors of crystallization.
