From Stoner to Local Moment Magnetism in Atomically Thin Cr2Te3

The field of two-dimensional (2D) ferromagnetism has been proliferating over the past few years, with ongoing interests in basic science and potential applications in spintronic technology. However, a high-resolution spectroscopic study of the 2D ferromagnet is still lacking due to the small size and air sensitivity of the exfoliated nanoflakes. Here, we report a thickness-dependent ferromagnetism in epitaxially grown Cr2Te3 thin films and investigate the evolution of the underlying electronic structure by synergistic angle-resolved photoemission spectroscopy, scanning tunneling microscopy, x-ray absorption spectroscopy, and first-principle calculations. A conspicuous ferromagnetic transition from Stoner to Heisenberg-type is directly observed in the atomically thin limit, indicating that dimensionality is a powerful tuning knob to manipulate the novel properties of 2D magnetism. Monolayer Cr2Te3 retains robust ferromagnetism, but with a suppressed Curie temperature, due to the drastic drop in the density of states near the Fermi level. Our results establish atomically thin Cr2Te3 as an excellent platform to explore the dual nature of localized and itinerant ferromagnetism in 2D magnets.

二维（2D）铁磁学领域在过去数年间蓬勃发展，基础科学研究与自旋电子学技术的潜在应用均持续受到广泛关注。然而，由于剥离得到的纳米薄片尺寸微小且对空气敏感，目前仍缺乏针对二维铁磁体的高分辨光谱学研究。本研究针对外延生长的Cr₂Te₃薄膜开展了厚度依赖的铁磁性研究，并协同采用角分辨光电子能谱（angle-resolved photoemission spectroscopy）、扫描隧道显微镜（scanning tunneling microscopy）、X射线吸收光谱（x-ray absorption spectroscopy）与第一性原理计算（first-principle calculations），系统探究了其内在电子结构的演化规律。在原子级超薄极限下，我们直接观测到了从斯通纳（Stoner）型到海森伯（Heisenberg）型的显著铁磁相变，这表明维度是调控二维磁性新奇特性的有效手段。单层Cr₂Te₃仍保持较强的铁磁性，但由于费米能级附近的态密度急剧下降，其居里温度被抑制。本研究结果证实，原子级超薄Cr₂Te₃是探究二维磁体中局域与巡游铁磁性双重特性的优质实验平台。