STEM Study of Structure and Local Short-Range Orders in the Fe_5−xGeTe₂ Crystals with Ferromagnetism Near Room Temperature

Van der Waals (vdW) bonded materials have historically attracted intense attention, due to their promise for advanced electronic and optical functionalities. Recently, magnetically-active vdW materials have been recognized as an important class of materials for realizing new physics and functionalities. Of the magnetic vdW materials, ferromagnetic Fe₃GeTe₂ has garnered significant attention for its high Curie temperature T_C ~230 K. Recently, a Fe_5-xGeTe₂ compound with thicker Fe-Ge slabs and stronger magnetism has been successfully obtained. As viewed by bulk diffraction, the material has a relatively large unit cell and contains intrinsic disorder. The nature of the local structure is anticipated to impact the Curie temperature, which ranges from 270–310K depending on processing conditions. As such, an atomic-scale probe of the local structures and compositions is essential for understanding the intrinsic magnetism in this vdW material.