Multiferroic materials have ignited enormous interest owing to their co-existence of ferroelectricity and ferromagnetism, which hold substantial promise for advanced device applications. However, the size effect, dangling bonds, and interface effect in traditional multiferroics severely hinder their potential in nanoscale device applications. Recent theoretical and experimental studies have evidenced the possibility of realizing two-dimensional (2D) multiferroicity in van der Waals (vdW) layered CuCrP₂S₆. However, the incorporation of magnetic Cr ions in the ferroelectric framework leads to antiferroelectric and antiferromagnetic orderings, while macroscopic spontaneous polarization is always absent. Herein, we report the direct observation of robust out-of-plane ferroelectricity in 2D vdW CuCrP₂S₆ at room temperature with a comprehensive investigation. Modification of the ferroelectric polarization states in 2D CuCrP₂S₆ nanoflakes is experimentally demonstrated. Moreover, external electric field-induced polarization switching and hysteresis loops are obtained in CuCrP₂S₆ down to ~2.6 nm (4 layers). By using atomically resolved scanning transmission electron microscopy, we unveil the origin of the emerged room-temperature ferroelectricity in 2D CuCrP₂S₆. Our work can facilitate the development of multifunctional nanodevices and provide important insights into the nature of ferroelectric ordering of this 2D vdW material.

多铁性材料由于铁电性和铁磁性的共存而引起了人们的极大兴趣，这为先进器件应用带来了巨大的希望。然而，传统多铁性材料中的尺寸效应、悬挂键和界面效应严重阻碍了它们在纳米级器件应用中的潜力。最近的理论和实验研究证明了在范德华（vdW）层状CuCrP ₂ S ₆中实现二维（2D）多铁性的可能性。然而，磁性Cr离子在铁电框架中的结合导致了反铁电和反铁磁有序化，而宏观自发极化始终不存在。在此，我们报告了在室温下直接观察到的二维 vdW CuCrP ₂ S ₆中鲁棒的面外铁电性并进行了全面的研究。实验证明了二维 CuCrP ₂ S ₆纳米片中铁电极化状态的改变。此外，在低至~2.6 nm（4 层）的CuCrP ₂ S ₆中获得了外部电场引起的偏振切换和磁滞回线。_{通过使用原子分辨扫描透射电子显微镜，我们揭示了二维 CuCrP 2} S ₆中出现的室温铁电性的起源。我们的工作可以促进多功能纳米器件的开发，并为这种二维 vdW 材料的铁电有序性质提供重要的见解。