K2cos2: A Two-Dimensional In-Plane Antiferromagnetic Insulator

Recent discovery of two-dimensional (2D) magnetic materials has brought magnetism to the flatland and opened up exciting opportunities for the exploration of fundamental physics as well as novel device applications. Here, we predict a thermodynamically stable 2D magnetic material, K2CoS2, which retains its in-plane bulk antiferromagnetic (AFM) order down to the monolayer and bilayer limits. Magnetic moments (2.5 mu(B)/Co) are found to form a quasi-one-dimensional antiferromagnetically ordered chain of Co atoms. The nonmagnetic electronic spectrum of the monolayer film is found to host flatbands and van Hove singularities, which play a key role in stabilizing the magnetic ground state. Based on classical Monte Carlo simulations, we estimate the Ned temperature for the AFM monolayer to be approximate to 15 K. Our study demonstrates that K2CoS2 hosts a robust AFM state which persists from the monolayer limit to the bulk material.