Charge-induced magnetic instability of atomically thin ferromagnetic semiconductors: The case of CrI3

Abstract

Recent studies have shown that the ferromagnetic intralayer order in $\mathrm{Cr}{\mathrm{I}}_{3}$ is weakened by electrostatic electron doping, with magnetization and Curie temperature decreasing linearly with doping density. The linear doping dependence observed in $n$-type $\mathrm{Cr}{\mathrm{I}}_{3}$ is puzzling because it requires a ``fine-tuned'' nonlinear decrease of the spin-wave gap upon electron doping. Here, using first-principles-based simulations, we reveal that electron doping of $\mathrm{Cr}{\mathrm{I}}_{3}$ induces a quantum phase transition to a magnetic state characterized by spontaneous spin-flip formation at the atomic scale. The electron localization in the presence of the spin-flips ``renormalizes'' the energy gap for collective spin excitations, which explains the puzzling doping effect on the two-dimensional magnetism of $\mathrm{Cr}{\mathrm{I}}_{3}$.