  The exploration of magnetism in two-dimensional layered materials has
attracted extensive research interest. For the monoclinic phase CrI3 with
interlayer antiferromagnetism, finding a static and robust way of realizing the
intrinsic interlayer ferromagnetic coupling is desirable. In this Letter, we
study the electronic structure and magnetic properties of the nonmagnetic
element (e.g., O, S, Se, N, P, As and C) doped bi- and triple-layer CrI3
systems via first-principles calculations. Our results demonstrate that O, P,
S, As, and Se doped CrI3 bilayer can realize interlayer ferromagnetism. Further
analysis shows that the interlayer ferromagnetic coupling in the doped
few-layer CrI3 is closely related to the formation of localized spin-polarized
state. This finding indicates that insulated interlayer ferromagnetism can be
realized at high doping concentration (larger than 8.33%). When the doping
concentration is less than 8.33%, but larger than 2.08%, an insulator-metal
phase transition can occur since the localized spin-polarized states percolate
to form contiguous grids in few-layer CrI3.
