K$_2$CoS$_2$: A new two-dimensional in-plane antiferromagnetic insulator

TL;DR

This paper predicts K$_2$CoS$_2$ as a stable 2D in-plane antiferromagnetic insulator with persistent magnetic order from monolayer to bulk, featuring flat bands and a Neel temperature around 15K.

Contribution

It introduces K$_2$CoS$_2$ as a new 2D magnetic material with robust in-plane antiferromagnetic order across different thicknesses.

Findings

K$_2$CoS$_2$ is thermodynamically stable in 2D form.

The material exhibits in-plane antiferromagnetic order down to monolayer.

The estimated Neel temperature for the monolayer is approximately 15K.

Abstract

The recent discovery of two-dimensional (2D) magnetic materials has brought magnetism to the flatland. This has opened up exciting opportunities for the exploration of fundamental physics as well as for novel device applications. Here, we predict a new thermodynamically stable 2D magnetic material, K$_2$CoS$_2$, which retains its in-plane anti-ferromagnetic order down to the monolayer and bilayer limits. We find that the magnetic moments ($2.5 \mu_B/$Co) are aligned along the intra-Co chains, from monolayer to bulk. The non-magnetic electronic spectrum of both the monolayer and bilayer films is found to host flat bands and van-Hove singularities, which in instrumental in giving rise to the the magnetic ground state. Based on classical Monte-Carlo simulations, we estimate the Neel temperature for the antiferromagnetic monolayer to be $\approx 15$K. Our study thus establishes that K$_2$CoS$_2$ hosts a robust antiferromagnetic state which persists from the monolayer limit to the bulk material.