Intrinsic ferromagnetism in epitaxial MnSe2 van der Waals monolayers at room temperature

Monolayer van der Waals (vdW) magnets provide an exciting opportunity for exploring two-dimensional (2D) magnetism for scientific and technological advances, but the intrinsic ferromagnetism has only been observed at low temperatures. Here, we report the observation of room temperature ferromagnetism in the monolayer limit for epitaxial MnSe₂ vdW layers. Since bulk Mn-Se compounds are not ferromagnetic and bulk van der Waals crystals of MnSe₂ do not exist, we rely on molecular beam epitaxy to epitaxially stabilize MnSe₂ layers. Magnetization measurements of monolayer films show ferromagnetic ordering with large saturation magnetization of ~ 4 Bohr magnetons per MnSe₂ formula unit, which is comparable to previous density functional theory calculations. Continued growth produces epitaxial a-MnSe/MnSe₂/GaSe heterostructures that have enhanced saturation magnetization and the emergence of a new x-ray diffraction peak consistent with expectations for vdW MnSe₂ provides strong evidence for multilayers of vdW MnSe₂ located at the interface between non-ferromagnetic a-MnSe and GaSe. These results establish the foundation for room temperature 2D ferromagnetism in large area epitaxial vdW magnets, which has potential application in energy efficient information storage and processing.