Discovery of stable and intrinsic antiferromagnetic iron oxyhalide monolayers.

Two-dimensional (2-D) antiferromagnetic (AFM) materials have shown promise over their ferromagnetic (FM) counterparts for developing advanced spintronic devices; however, they have been rarely found with high Néel temperatures to date. Here, by employing first-principles calculations and Monte Carlo simulations, we demonstrate that the family of 2-D iron oxyhalides monolayers, FeOX (X = F, Cl, Br, I), are magnetic Mott insulators with their AFM ground state possessing relatively high Néel temperatures. The structural stabilities of the FeOX monolayers are proved using a set of phonon, molecular dynamics, and elastic constant calculations. The calculated Néel temperature of the FeOCl monolayer is close to that of FeOCl bulk because of the weak van der Waals interaction between the layers. More importantly, the predicted Néel temperatures of FeOX (X = F, Cl, Br, I) monolayers can be increased by biaxial compression strain. The Néel temperature of the strained FeOF and FeOI monolayers can approach 200 K, which suggests that they can be robust antiferromagnets with relatively high Néel temperatures compared with other available 2-D magnets. Our calculations show that both the in-plane and the inter-plane magnetic interactions affect the AFM coupling between Fe atoms in FeOX monolayers. The easy axis of the 2-D FeOX is found to be along the in-plane direction. The FeOX monolayers may provide an excellent platform for building novel spintronic devices at the nanoscale.