2D Janus MnSX (X= Cl, Br, I) Monolayers with Intrinsic Ferromagnetism and Half-Metallicity

Using the first-principles calculations, we have investigated the structural, electronic, and magnetic properties of the two-dimensional Janus MnSX (X= Cl, Br, I) monolayers. The dynamical stability for the 2D Janus monolayers has been confirmed by phonon spectrum calculation. Also, all manganese sulfide halide monolayers show half-metal with 100% spin polarization and a wide half-metallic gap. The noncollinear DFT calculations indicate that the two-dimensional Janus monolayers are ferromagnetically ordered systems and the preferred direction of magnetization lies in-plane of Janus manganese sulfide halide monolayers. The magnetic anisotropy energy increases from MnSCl to MnSI, related to the strong spin-orbit coupling at the I atom and the increased asymmetry between the sulfide and halide planes. The dispersion relation of magnetic excited states is obtained by applying the linear order Holstein–Primakoff transformation to the anisotropic Heisenberg Hamiltonian. We estimated Curie temperature for the monolayers by a self-consistent calculation of magnetization as a function of temperature. Our study presents a new class of 2D magnetic materials for future spintronics and valleytronics.