Origin of itinerant ferromagnetism in two-dimensional Fe₃GeTe₂

Magnetic order in two-dimensional systems was not supposed to exist at finite temperature. In recent years, the successful preparation of two-dimensional ferromagnetic materials such as CrI₃, Cr₂Ge₂Te₆, and Fe₃GeTe₂ opens up a new chapter in the remarkable field of two-dimensional materials. Here, we report on a theoretical analysis of the stability of ferromagnetism in Fe₃GeTe₂. We uncover the mechanism of holding long-range magnetic order and propose a model to estimate the Curie temperature of Fe₃GeTe₂. Our results reveal the essential role of magnetic anisotropy in maintaining the magnetic order of two-dimensional systems. The theoretical method used here can be generalized to future research of other magnetic two-dimensional systems.