Ferromagnetism of Molecular Beam Epitaxy-grown Ultra-thin Cr2Ge2Te6 Films Down to the Monolayer Limit on Si Substrates.

Cr2Ge2Te6, a prototypical van der Waals (vdW) ferromagnetic semiconductor, has attracted significant interest for its potential applications in high-performance spintronics. However, the magnetic ground state of monolayer Cr2Ge2Te6 remains elusive due to fragile and irregularly shaped thin flake samples with weak magnetic signals. Here, we successfully grow Cr2Ge2Te6 films down to one monolayer by molecular beam epitaxy. By exploiting a self-limiting growth mode, we achieve uniform monolayer Cr2Ge2Te6 films across entire millimeter-scale Si substrates. Through a combination of superconducting quantum interference device magnetometry and anomalous Hall effect measurements, we establish that monolayer Cr2Ge2Te6 exhibits intrinsic ferromagnetism with perpendicular magnetic anisotropy below 10 K, albeit with strong magnetic fluctuations characteristic of its 2D nature. Furthermore, a systematic thickness-dependent study reveals that a crossover from this fluctuation-dominated 2D magnetism turns into conventional long-range ferromagnetic order as the film thickness increases. Our work not only definitively establishes the intrinsic ferromagnetic ground state of monolayer Cr2Ge2Te6, but also provides a scalable, silicon-compatible route for preparing the 2D magnet for future spintronic or quantum devices.