Magnetic Skyrmionic Bubbles at Room Temperature and Sign Reversal of the Topological Hall Effect in a Layered Ferromagnet Cr_0.87Te

The search for materials that exhibit topologically protected spin configurations, such as magnetic skyrmions, continues to be fueled by the promise of outstanding candidate components for spin-based applications. In this study, in situ Lorentz transmission electron microscopy directly images Bloch-type magnetic skyrmionic bubbles in a layered ferromagnet Cr0.87Te single crystal. Owing to the competition between a magnetic dipole interaction and uniaxial easy axis anisotropy, nanoscale magnetic bubbles with random chirality can be observed in a wide temperature range covering room temperature when the external magnetic field is applied along the out-of-plane direction. Moreover, high-density and stable skyrmionic bubbles are successfully realized at zero magnetic field by appropriate field-cooling manipulation. Additionally, a sign reversal of the Hall effect and the derived topological Hall effect is observed and discussed. As quasi-two-dimensional materials, the binary chromium tellurides hosting magnetic skyrmions could have many applications in low-dimensional skyrmion-based spintronic devices in an ambient atmosphere.探索具有拓扑保护自旋构型（topologically protected spin configurations）的材料——例如磁斯格明子（magnetic skyrmions）——始终因有望成为自旋基应用的优质候选组件而备受关注。本研究中，研究人员借助原位洛伦兹透射电子显微镜（in situ Lorentz transmission electron microscopy），直接对层状铁磁体（layered ferromagnet）Cr₀.₈₇Te单晶中的布洛赫型磁斯格明子泡（Bloch-type magnetic skyrmionic bubbles）进行成像。由于磁偶极相互作用（magnetic dipole interaction）与单轴易轴各向异性（uniaxial easy axis anisotropy）之间的竞争，当外磁场沿垂直于样品平面方向施加时，在涵盖室温的宽温度区间内均可观察到具有随机手性（chirality）的纳米级磁泡。此外，通过合理的场冷却调控（field-cooling manipulation），可在零磁场下实现高密度且稳定的磁斯格明子泡。研究还观察并讨论了霍尔效应（Hall effect）及其衍生的拓扑霍尔效应（topological Hall effect）的符号反转现象。作为准二维材料（quasi-two-dimensional materials），承载磁斯格明子的二元碲化铬（binary chromium tellurides）有望在大气环境下的低维磁斯格明子基自旋电子器件（spintronic devices）中获得诸多应用。