Theoretical prediction of 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 [1]. Magnetic moments (2.5 μ_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 Neel temperature for the AFM monolayer to be ≈ 15 K. Our study demonstrates that K₂CoS₂ hosts a robust AFM state which persists from the monolayer limit to the bulk material.

[1] Anan Bari Sarkar et. al, Phys. Rev. B 102, 035420 (2020).