Interface-Induced Stability of Nontrivial Topological Spin Textures: Unveiling Room-Temperature Hopfions and Skyrmions
Topological spin configurations, such as soliton-like spin texture and Dirac electron assemblies, have emerged in recent years in both fundamental science and technological applications. Achieving stable topological spin textures at room-temperature is crucial for enabling these structures as long-range information carriers. However, their creation and manipulation processes have encountered difficulties due to multi-step field training techniques and competitive interactions. Thus, a spontaneous ground state for multi-dimensional topological spin textures is desirable, as skyrmions form swirling, hedgehog-like spin structures in two dimensions, while hopfions emerge as their twisted three-dimensional counterparts. Here, we report the first observation of robust and reproducible topological spin textures of hopfions and skyrmions observed at room temperature and in zero magnetic field, which are stabilized by geometric confinement and protected by interfacial magnetism in a ferromagnet/topological insulator/ferromagnet trilayer heterostructure. These skyrmion-hopfion configurations are directly observed at room temperature with Lorenz transmission electron microscopy. Using micromagnetic modelling, the experimental observations of hopfion-skyrmion assemblies are reproduced. Our model reveals a complete picture of how spontaneously organized skyrmion lattices encircled by hopfion rings are controlled by surface electrons, uniaxial anisotropy and Dzyaloshinskii-Moriya interaction, all at ambient temperature. Our study provides evidence that topological chiral spin textures can facilitate the development of magnetically defined information carriers. These stable structures hold promise for ultralow-power and high-density information processing, paving the way for the next generation of topologically defined devices.