Quaternary-Digital Data Storage Based on Magnetic Bubbles in Anisotropic Materials

Topologically nontrivial nanowhirls, called magnetic skyrmions, are often considered attractive for spintronic applications like racetrack data storage devices. 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 Dzyaloshinskii-Moriya interaction, 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 that of topologically nontrivial spin textures. This allows the construction of a quaternary-digit-based racetrack storage device that overcomes the two mentioned drawbacks of skyrmion-based racetracks.