  The migration of grain boundaries leads to grain growth in polycrystals and
is one mechanism of grain-boundary-mediated plasticity, especially in
nanocrystalline metals. This migration is due to the movement of
dislocation-like defects, called disconnections, which couple to externally
applied shear stresses. While this has been studied in detail in recent years,
the active disconnection mode was typically associated with specific
macroscopic grain boundary parameters. We know, however, that varying
microscopic degrees of freedom can lead to different atomic structures without
changing the macroscopic parameters. These structures can transition into each
other and are called complexions. Here, we investigate $[11\overline{1}]$
symmetric tilt boundaries in fcc metals, where two complexions -- dubbed domino
and pearl -- were observed before. We compare these two complexions for two
different misorientations: In $\Sigma19$b $[11\overline{1}]$ $(178)$
boundaries, both complexions exhibit the same disconnection mode. The critical
stress for nucleation and propagation of disconnections is nevertheless
different for domino and pearl. At low temperatures, the Peierls-like barrier
for disconnection propagation dominates, while at higher temperatures the
nucleation is the limiting factor. For $\Sigma$7 $[11\overline{1}]$ $(145)$
boundaries, we observed a larger difference. The domino and pearl complexions
migrate in different directions under the same boundary conditions. While both
migration directions are possible crystallographically, an analysis of the
complexions' structural motifs and the disconnection core structures reveals
that the choice of disconnection mode and therefore migration direction is
directly due to the atomic structure of the grain boundary.
