Two-Dimensional Co2S2 monolayer with robust ferromagnetism

Design and synthesis of two-dimensional (2D) materials with robust intrinsic ferromagnetism is highly desirable due to their potential applications in spintronics devices. In this work, we identify a new 2D cobalt sulfide (Co₂S₂) material by using first-principles calculations and particle swarm optimization (PSO) global structure search. We show that the 2D Co₂S₂ is most stable in the litharge type tetragonal structure with space group of P4/nmm. The elastic constants, phonon spectrum, and molecular dynamics simulation confirm its mechanical, dynamical and thermal stability, respectively. It is also found that Co₂S₂ monolayer is a ferromagnetic metal with a Curie temperature up to 404 K. In addition, we propose a feasible procedure to synthesize the Co₂S₂ monolayer by chemically exfoliating from bulk TlCo₂S₂ phase.