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

TL;DR

This study demonstrates the successful growth and characterization of monolayer Cr2Ge2Te6 films exhibiting intrinsic ferromagnetism, providing insights into their magnetic properties and a scalable fabrication method for potential spintronic applications.

Contribution

We achieved uniform monolayer Cr2Ge2Te6 films via molecular beam epitaxy and established their intrinsic ferromagnetic ground state with perpendicular anisotropy.

Findings

Monolayer Cr2Ge2Te6 exhibits intrinsic ferromagnetism below ~10 K.

A thickness-dependent crossover from 2D magnetic fluctuations to long-range order.

Scalable, silicon-compatible growth method for 2D ferromagnetic films.

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.