  Chiral domain walls of Neel type emerge in heterostructures that include
heavy metal (HM) and ferromagnetic metal (FM) layers owing to the
Dzyaloshinskii-Moriya (DM) interaction at the HM/FM interface. In developing
storage class memories based on the current induced motion of chiral domain
walls, it remains to be seen how dense such domain walls can be packed
together. Here we show that a universal short range repulsion that scales with
the strength of the DM interaction exists among chiral domain walls. The
distance between the two walls can be reduced with application of out of plane
field, allowing formation of coupled domain walls. Surprisingly, the current
driven velocity of such coupled walls is independent of the out of plane field,
enabling manipulation of significantly compressed coupled domain walls using
current pulses. Moreover, we find that a single current pulse with optimum
amplitude can create a large number of closely spaced domain walls. These
features allow current induced generation and synchronous motion of highly
packed chiral domain walls, a key feature essential for developing domain wall
based storage devices.
