Origin of ferromagnetism in Fe3GeTe2 and its manipulation
Recent experimental findings of two dimensional ferromagnetism in Fe3GeTe2, whose critical temperature can reach room temperature by gating, has attracted great research interests. Here we performed the elaborate ab-initio studies by using density functional theory, dynamical mean-field theory and magnetic force response theory. Contrary to the conventional wisdom, it is unambiguously shown that Fe3GeTe2 is not ferromagnetic but antiferromagnetic carrying zero net moment in its stoichiometric phase. Fe defect and hole doping are the keys to make this material ferromagnetic as supported by unnoticed previous experiments. Further, we found that the electron doping also induces the antiferro- to ferromagnetic transition. It is a crucial factor to understand the notable recent experiment of gate-controlled ferromagnetism. Our results not only unveil the origin of ferromagnetism of this material but also show how it can be manipulated with defect and doping.