Magnetic polaron and antiferromagnetic-ferromagnetic transition in doped bilayer CrI3

Gate-induced magnetic switching in bilayer CrI₃ has opened new ways for the design of novel low-power magnetic memories based on van der Waals heterostructures. The proposed switching mechanism seems to be fully dominated by electrostatic doping. Here we explain, by first-principles calculations, the ferromagnetic transition in doped bilayer CrI₃. For the case of a very small electron doping, our calculations predict the formation of magnetic polarons ("ferrons," "fluctuons") where the electron is self-locked in a ferromagnetic droplet in an antiferromagnetic insulating matrix. The self-trapping of holes is impossible, at least within our approximation. Our findings could explain the recently observed asymmetric magnetic switching in dual-gated bilayer CrI₃; for electron doping the formation of magnetic polarons facilitates the antiferro-to-ferro phase transition; for holes the transition takes place without any intermediate state requiring a higher doping level.