Pressure-induced ferromagnetism and enhanced perpendicular magnetic anisotropy of bilayer CrI.

Using the first principles calculations, we explored the pressure dependent magnetic properties of CrI bilayer for AB and AA type stacking. We found an anti-ferromagnetic (AFM) ground state in both pristine bilayer systems with indirect band gaps of 1.71 and 1.68 eV for AB and AA type system. However, the transition from AFM to ferromagnetic (FM) state was achieved with the pressure and the band gap was decreased although the indirect band gap nature remains unchanged. We obtained a substantially enhanced perpendicular magnetic anisotropy with pressure. In the pristine AFM bilayer, both Cr and iodine atoms almost equally contributed to the perpendicular magnetic anisotropy. However, the contribution from the iodine atoms was almost four times larger than the Cr contribution with increasing the pressure. Particularly, the interface iodine atoms played a major role for the enhancement of the perpendicular magnetic anisotropy. We found that both AB and AA type bilayer displayed the same tendency.