  Magnetic skyrmions have been the focus of intense research with promising
applications in memory, logic and interconnect technology. Several schemes have
been recently proposed and demonstrated to nucleate skyrmions. However, they
either result in an uncontrolled skyrmion bubble production or are mostly
targeted towards integration with racetrack memory device. In this work, we
propose a novel scheme for a controlled single skyrmion nucleation in a
confined nanowire geometry with sub-100 nm width using a generalized approach
of "localized spin current injection" technique in material systems exhibiting
low Dzyaloshinskii-Moriya interaction (DMI). Our proposed nucleation mechanism
follows a pathway involving the creation of a reversed magnetic domain
containing one or more pairs of vertical Bloch lines (VBLs) that form an
edge-to-edge domain wall as the VBLs get annihilated at the edge of the
nanowire. However, pinning of the edge domain walls within a narrow gap using
notches or anti-notches results in the creation of a magnetic bubble with
defect-free domain wall that eventually relaxes into a circular skyrmion
structure. Our simulations predict that the proposed mechanism allows skyrmion
nucleation on sub-nanosecond timescale, shows robustness to variations like
local pinning sites and is applicable for any skyrmion-based logic, memory and
interconnect application.
