The emergent magnetic two-dimensional (2D) materials provide ideal solid-state platforms for a broad range of applications including miniaturized spintronics, nonreciprocal optics, and magnetoelectric sensors. Owing to the general environmental sensitivity of 2D magnets, the understanding of ambient effects on 2D magnetism is critical. Apparently, the nature of itinerant ferromagnetism potentially makes metallic 2D magnets insensitive to environmental disturbance. Nevertheless, our systematic study showed that the Curie temperature of metallic 2D Fe₃GeTe₂ decreases dramatically in the air but thick Fe₃GeTe₂ exhibits self-protection. Remarkably, we found the air exposure effectively promotes the formation of multiple magnetic domains in 2D Fe₃GeTe₂, but not in bulk Fe₃GeTe₂. Our first-principles calculations support the scenario that substrate-induced roughness and tellurium vacancies boost the interaction of 2D Fe₃GeTe₂ with the air. Our elucidation of the thickness-dependent air-catalyzed evolution of Curie temperatures and magnetic domains in 2D magnets provides critical insights for chemically decorating and manipulating 2D magnets.

新兴的磁性二维 (2D) 材料为广泛的应用提供了理想的固态平台，包括微型自旋电子学、非互易光学和磁电传感器。由于 2D 磁体的一般环境敏感性，了解环境对 2D 磁性的影响至关重要。显然，流动铁磁性的性质可能使金属二维磁铁对环境干扰不敏感。尽管如此，我们的系统研究表明，金属二维 Fe ₃ GeTe ₂的居里温度在空气中急剧下降，但厚 Fe ₃ GeTe ₂表现出自我保护。值得注意的是，我们发现空气暴露有效地促进了二维 Fe ₃ GeTe ₂中多个磁畴的形成，但在块状 Fe ₃ GeTe _{2 中没有}。我们的第一性原理计算支持基板引起的粗糙度和碲空位促进 2D Fe ₃ GeTe ₂与空气相互作用的情况。我们对二维磁体中居里温度和磁畴的厚度依赖空气催化演变的阐明为化学装饰和操作二维磁体提供了重要的见解。