Reaching above room-temperature ferromagnetism in scalable, ultrathin 2D magnets grown by molecular-beam epitaxy

The recent discovery of intrinsic magnetism in two-dimensional materials has raised an enormous fundamental interest, as their stable ground state challenges the classical laws of low-dimensional magnetism. However, a robust 2D ferromagnet which is stable above room-temperature has not been achieved yet, a hard-sought building block to envision spintronic device applications based on 2D magnets. Moreover, most of the 2D magnets reported to date are prepared by the exfoliation method, which limits the scalability for industrial applications. Here, we propose to investigate a room-temperature 2D magnet down to the monolayer limit, Fe5GeTe2, which is grown by molecular-beam epitaxy and thus provides robust magnetic properties and scalability at the same time. Preliminary results show a sizable XMCD hysteresis loop at room temperature of Fe5GeTe2 in the ultrathin regime (5nm) when it is grown on Bi2Se3 by van der Waals epitaxy. In this proposal, we aim to thoroughly investigate the high-temperature magnetic properties of Fe5GeTe2 on Bi2Se3 in the few-layer and monolayer regime. The determination of the Curie-Temperature (Tc) as a function of layer number is of utmost importance to verify whether the high Tc persist down to the truly 2D (monolayer) limit. Secondly, we aim to find out the effect of the topological insulator Bi2Se3 as a substrate in the high Tc properties of F5GT. By comparing it with Fe5GeTe2 grown on standard, inert substrates such as Al2O3 (0001), we want to elucidate whether interface phenomena at TI/2D FM system play any role on strengthening the magnetic properties of the 2D layer.