Revealing the origin of high-temperature ferromagnetism in two-dimensional Fe5GeTe2 epitaxial thin films

Two-dimensional magnetic materials have recently sparked a lot of interest, but some important challenges need to be overcome in order to unlock their application potential. One of those is to synthesize a 2D ferromagnet which shows robust magnetic properties above room-temperature, and another one is to prepare homogeneous, scalable layers only few-atoms thick. Here, we explore the magnetic properties of a high-temperature 2D magnet, Fe5GeTe2, which is grown by molecular-beam epitaxy and thus provides robust magnetism and scalability at the same time. Previous results show a sizable XMCD hysteresis loop above room-temperature of Fe5GeTe2 when it is grown on Bi2Te3 by van der Waals epitaxy. In this proposal, we aim to thoroughly investigate the origin of the high-temperature magnetic properties of optimized Fe5GeTe2 films on Bi2Te3 in the few-layer and monolayer regime. The determination of the Curie-Temperature (Tc) via XMCD as a function of layer number is of utmost importance to verify whether the high Tc persist down to the truly 2D (monolayer) limit. In the few-layer regime, where the high Tc is readily demonstrated, we aim to look at structural/orbital distortions via angular-dependent XAS/XLD measurements, which are typically present in epitaxially grown ultrathin films. Consequently, the correlation between distortions in the crystalline unit cell and the strength of the magnetic exchange will be assessed in a single X-ray absorption-based experiment.