  The topologically non-trivial nano-whirls, called magnetic skyrmions, are
often considered attractive for spintronic applications like the racetrack data
storage device. However, skyrmions do not move parallel to applied currents and
typically do not coexist with other nano-objects, making the realization of
such storage concepts difficult. Herein we consider materials with an
anisotropic DMI, like tetragonal Heusler materials, and show that four distinct
types of topologically trivial bubbles can coexist. We show that each of them
can be written by spin torques and that they can be distinguished using a
single magnetic tunneling junction. Due to their trivial topology, the four
types of bubbles move parallel to applied electrical currents and remain
equidistant under motion. Still, the bubbles have a small size and high
stability comparable to topologically non-trivial spin textures. This allows to
construct a quaternary-digit-based racetrack storage device that overcomes the
two mentioned drawbacks of skyrmion-based racetracks.
