Magnetic properties of molecular beam epitaxy-grown ultrathin Cr2Ge2Te6 films down to monolayer limit on Si substrates

Abstract

Cr2Ge2Te6, a prototypical van der Waals ferromagnetic semiconductor, have 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 irregular-shaped thin flake samples with weak magnetic signals. Here, we successfully grow uniform ferromagnetic Cr2Ge2Te6 films down to monolayer by molecular beam epitaxy. By exploiting a self-limiting growth mode, we achieve synthesis of 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 two-dimensional nature. Furthermore, a systematic thickness-dependent study reveals a crossover from this fluctuation-dominated two-dimensional 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 two-dimensional magnet for future spintronic or quantum devices.