Epitaxial van der Waals heterostructures of Cr2Te3 on two-dimensional materials

Abstract

Achieving large-scale growth of two-dimensional (2D) ferromagnetic materials with high Curie temperature ${T}_{\mathrm{C}}$ and perpendicular magnetic anisotropy (PMA) is highly desirable for the development of ultracompact magnetic sensors and magnetic memories. In this context, van der Waals (vdW) ${\mathrm{Cr}}_{2}{\mathrm{Te}}_{3}$ appears to be a promising candidate. Bulk ${\mathrm{Cr}}_{2}{\mathrm{Te}}_{3}$ exhibits strong PMA and a ${T}_{\mathrm{C}}$ of 180 K. Moreover, both PMA and ${T}_{\mathrm{C}}$ might be adjusted in ultrathin films by engineering composition or strain or applying an electric field. In this work, we demonstrate the molecular beam epitaxy (MBE) growth of vdW heterostructures of five-monolayer quasifreestanding ${\mathrm{Cr}}_{2}{\mathrm{Te}}_{3}$ on three classes of 2D materials: graphene (semimetal), ${\mathrm{WSe}}_{2}$ (semiconductor), and ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ (topological insulator). By combining structural and chemical analysis down to the atomic level with ab initio calculations, we confirm the single-crystalline character of ${\mathrm{Cr}}_{2}{\mathrm{Te}}_{3}$ films on the 2D materials with sharp vdW interfaces. They all exhibit PMA and ${T}_{\mathrm{C}}$ close to the bulk ${\mathrm{Cr}}_{2}{\mathrm{Te}}_{3}$ value of 180 K. Ab initio calculations confirm this PMA and show how its strength depends on strain. Finally, Hall measurements reveal a strong anomalous Hall effect, which changes sign at a given temperature. We theoretically explain this effect by a sign change of the Berry phase close to the Fermi level. This transition temperature depends on the 2D material in proximity, notably as a consequence of charge transfer. MBE-grown ${\mathrm{Cr}}_{2}{\mathrm{Te}}_{3}$/2D material bilayers constitute model systems for the further development of spintronic devices combining PMA, large spin-orbit coupling, and sharp vdW interface.