Above Room Temperature Ferromagnetism in Epitaxial Thin Films of the Layered Ternary Chalcogenides Fe₅GeTe₂ and Fe₃GaTe₂

Layered magnetic materials are promising building blocks for the realization of ultra-compact spintronic devices. Moreover, combining them with other layered crystals to form the so-called van der Waals (vdW) heterostructures is a very attractive route to realize hybrid systems exhibiting integrated electronic, optical, and magnetic functionalities. So far, most of the experimental research on layered magnets and related vdW heterostructures has been conducted utilizing micrometer-sized flakes exfoliated from bulk single crystals. However, the implementation of these materials in various technologies depends strongly on the development of bottom-up, scalable synthesis approaches allowing to realize highly uniform films with well-defined interfaces. It also requires that each material component of the heterostructure remains functional, which ideally includes magnetic order above room temperature for the magnetic materials. Among different candidates, the ternary transition metal chalcogenides Fe_5-xGeTe₂ (FGeT, x ~ 0) and Fe₃GaTe₂ (FGaT) show a great potential due to their relatively high Curie temperature and highly tunable properties. Both materials possess a layered vdW structure with each single layer being formed of Fe and Ge (Ga) slabs encapsulated by layers of Te.<br/>In this talk, I will report on our results on epitaxial growth of FGeT and FGaT thin films on substrates such as single crystalline graphene (on SiC) and WSe₂ (on Al₂O₃) via molecular beam epitaxy. Structural characterization using different methods reveals the formation of high-quality crystalline films with sharp interfaces to the underlying templates. Importantly, magneto-transport and magnetometry measurements reveal ferromagnetic order persisting above 350 K with a predominant out-of-plane anisotropy for both FGeT and FGaT films. I will discuss the correlation between structure and magnetism, in particular the effect of thickness and Fe composition tuning on the magneto-transport properties of the films. These results represent an important advance beyond non-scalable flake exfoliation from bulk crystals, thus marking a crucial step towards the implementation of ferromagnetic chalcogenides in practical applications.