  We show that the coupling between two ferromagnetic layers separated by a
nonmagnetic spacer can be used to control the depinning of domain walls and
induce unidirectional domain wall propagation. We investigated CoFeB/Ti/CoFeB
trilayers where the easy axis of the magnetization of the top CoFeB layer is
out-of-plane and that of the bottom layer is in-plane. Using Magneto-optic Kerr
effect microscopy, we find that the depinning of a domain wall in the
perpendicularly magnetized CoFeB layer is influenced by the orientation of the
magnetization of the in-plane layer, which gives rise to a field-driven
asymmetric domain expansion. This effect occurs due to the magnetic coupling
between the internal magnetization of the domain wall and the magnetization of
the in-plane CoFeB layer, which breaks the symmetry of up-down and down-up
homochiral N\'eel domain walls in the perpendicular CoFeB layer. Micromagnetic
simulations support these findings by showing that the interlayer coupling
either opposes or favors the Dzyaloshinskii-Moriya interaction in the domain
wall, thereby generating an imbalance in the depinning fields. This effect also
allows for artificially controlling the chirality and dynamics of domain walls
in magnetic layers lacking a strong Dzyaloshinskii-Moriya interaction.
