Thermal fluctuation of Fe-Ge ordering in Fe5-xGeTe2 single crystals

Abstract

Fe_5-xGeTe₂ is a magnetic van der Waals material with a relatively high Curie temperature near room temperature. Fe_5-xGeTe₂ exhibits unique magnetic properties due to its chemical and structural complexities. In this study, we employed scanning tunneling microscopy (STM) to investigate the thermal fluctuation of Fe-Ge ordering in Fe_5-xGeTe₂. At low temperatures (79 K), the Fe_5-xGeTe₂ surface exhibits distinct order with √3 × √3 periodicity resulting from the ordered Fe(1) atoms located in the outermost Fe₅Ge sublayer, while Fe deficient area shows 1 × 1 hexagonal lattice. At room temperature, on the other hand, structural fluctuations occur as thermal energy drives Fe(1) atom diffusion via a vacancy-mediated process. This results in the temporal rearrangement of the √3 × √3 and 1 × 1 regions at their boundaries. These findings provide important insights into the structural and magnetic properties of Fe_5-xGeTe₂.