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

Abstract

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.