Temperature- and Field-Dependent Study of Magnetic Textures and Skyrmions in a Layered Van der Waals Magnet

Two-dimensional Van der Waals magnets offer a highly tunable platform for the study of novel topological textures such as skyrmions. Co-doped Fe₅GeTe₂ (FCGT) is such a system which exhibits zero-field, room temperature skyrmions when doped to precisely 50% Co concentration. The presence, structure, and organization of these skyrmions is highly dependent on sample geometry and environmental conditions and history. Previous study and simulation of this system have demonstrated stripe domains, isolated skyrmions, and skyrmion lattice at a variety of temperature and field conditions. Here, we use Lorentz transmission electron microscopy (LTEM) to map the behavior of magnetic domain structure in FCGT nanoflakes with temperature and applied field at a variety of nanoflake thicknesses. LTEM allows for domain imaging with in-situ temperature control from 90K to room temperature and field control from field-free conditions to well above the saturation magnetization of the system. The resulting temperature-magnetic field phase diagrams prescribe the necessary conditions to achieve magnetic skyrmions in FCGT.