  Ultrathin ferromagnetic strips with high perpendicular anisotropy have been
proposed for the development of memory devices where the information is coded
in tiny domains separated by domain walls. The design of practical devices
requires creating, manipulating and detecting domain walls in ferromagnetic
strips. Recent observations have shown highly efficient current-driven domain
wall dynamics in multilayers lacking structural symmetry, where the walls adopt
a chiral structure and can be driven at high velocities. However, putting such
a device into practice requires the continuous and synchronous injection of
domain walls as the first step. Here, we propose and demonstrate an efficient
and simple scheme for nucleating domain walls using the symmetry of the spin
orbit torques. Trains of short sub-nanosecond current pulses are injected in a
double bit line to generate a localized longitudinal Oersted field in the
ferromagnetic strip. Simultaneously, other current pulses are injected through
the heavy metal under the ferromagnetic strip. Notably, the Slonczewski-like
spin orbit torque assisted by the Oersted field allows the controlled injection
of a series of domain walls, giving rise to a controlled manner for writing
binary information and, consequently, to the design of a simple and efficient
domain wall shift register.
