Tuning the Magnetism in Ultrathin CrxTey Films by Lattice Dimensionality

2D magnetic crystals with atomic thickness exhibit intriguing physical properties, which have attracted considerable research interest in the related materials’ family, both in fundamental research and in developing spintronic devices. The recent discovery of some non-van der Waals 2D magnetic crystals expands the systems. Nevertheless, the relationship between the dimensionality of microscopic magnetic exchange interactions and macroscopic magnetic properties at the 2D limit remains to be fully elucidated. Here, we have fabricated mono-phased continuous ultrathin CrTe₂ and Cr₃Te₄ films by molecular beam epitaxy and elucidated the diverse magnetism tuned by the dimensionality of exchange interactions by a joint study of spin-polarized scanning tunneling microscopy, magnetization, magneto-transport measurements, and density functional theory calculations. The transition from a zigzag-antiferromagnetic order in the monolayer CrTe₂ to a ferromagnetic (FM) order in the second-layer CrTe₂ is confirmed, which is driven by their varied in-plane lattice constants induced change of 2D exchange interactions. A robust FM state with large perpendicular magnetic anisotropy in Cr₃Te₄ is observed, originating from its strong 3D exchange interactions. The observed evolution of magnetism demonstrates that the dimensionality of magnetic exchange interactions strongly influences magnetism even at the 2D limit.