Manipulating Chiral Spin Textures in Compensated Ferrimagnets

A promising approach to encode bits of information for next-generation memory and logic is by using solitons, such as domain walls (DW) or topological skyrmions, which can be translated by currents across racetrack-like wire devices. One technological and scientific challenge is to stabilize small spin textures and to move them efficiently with high velocities, which is critical for dense, fast memory and logic. However, in ferromagnetic materials, current-driven spin texture dynamics faced a “speed limit” of a few hundred m/s, and room-temperature-stable magnetic skyrmions were an order of magnitude too large to be useful in any competitive technologies. These problems were rooted in two fundamental characteristics of ferromagnets: large stray fields, which limit packing density, and precessional dynamics, which limit speed. By using a broader class of compensated metallic and insulating ferrimagnets, fundamental limits plaguing ferromagnets can be overcome. Here, we engineer chiral ferrimagnets with reduced magnetization (M) and angular momentum (S) to realize order of magnitude improvements in bit size and speed. In metallic, ferrimagnetic Pt/GdCo/TaOx films with sizeable Dzyaloshinskii–Moriya interaction, we realize current-driven DW motion of 1.3 km/s near the angular momentum compensation temperature and room-temperature-stable skyrmions with ~10 nm diameters near the magnetic compensation temperature. Moreover, by exploiting reduced S and low-dissipation in insulating garnets, we drive DWs to their relativistic limit using, achieving velocities in excess of 4300 m/s. We observe key signatures of relativistic motion including Lorentz contraction and velocity saturation. The experimental results are well-explained through analytical and atomistic modeling. These observations provide insight into the fundamental limits of magnetic soliton dynamics and establish a readily-accessible experimental framework to study relativistic solitonic physics.