Magnetic structure and exchange interactions of transition metal dihalide monolayers: First-principles studies

Based on the first-principles linear response method and Monte Carlo simulation, we investigate the magnetic properties of single-layer transition metal dihalides MX2 (M = V, Cr, Mn, Fe, Co, Ni; X = Cl, Br, I). We calculate the magnetic exchange interactions using the first-principles linear response method and find that the thirdnearest-neighbor interaction of most dihalides is very important. When spin-orbit coupling is included, FeX2 and CrX2 (X = Cl, Br, I) are predicted to be insulators. Using the parameters of the exchange interactions and magnetic anisotropy, the magnetic ground states of transition metal dihalide monolayers are obtained by Monte Carlo simulation. Moreover, we find that the magnetic ground states of ten MX2 monolayers are independent of the U value. Among them, the magnetic ground state of CrI2 is ferromagnetic, the magnetic ground state of CrCl2 is collinear antiferromagnetic, the magnetic ground states of VCl2, FeI2, and CoX2 (X = Br, I) are 120 antiferromagnetic, and the magnetic ground states of FeCl2 and NiX2 (X = Cl, Br, I) are helimagnetic.