Adsorption tuning of polarity and magnetism in AgCr2S4 monolayer

As a recent successfully exfoliated non van der Waals layered material, AgCrS2 has received a lot of attentions. Motivated by its structure related magnetic and ferroelectric behavior, a theoretical study on its exfoliated monolayer AgCr2S4 has been carried out in the present work. Based on density functional theory, the ground state and magnetic order of monolayer AgCr2S4 have been determined. The centrosymmetry emerges upon two-dimensional confinement and thus eliminates the bulk polarity. Moreover, two-dimensional ferromagnetism appears in the CrS2 layer of AgCr2S4 and can persist up to room temperature. The surface adsorption has also been taken into consideration, which shows a nonmonotonic effect on the ionic conductivity through ion displacement of the interlayer Ag, but has little impact on the layered magnetic structure.