Strain tunable magnetism in SnX₂ (X = S, Se) monolayers by hole doping

By first-principles calculations, the magnetism of hole doped tin dichalcogenides SnX₂ (X = S, Se) monolayers is systematically studied. It is found that a phase transition from nonmagnetic to ferromagnetic ground state appears once above the critical hole density (~10¹⁴ cm^-2). The spin magnetic moment can maintain a magnitude of 1.0 μ_B/hole with excellent stability of ferromagnetic state. Furthermore, we demonstrate that strain is very useful to modulate the DOS near the valence band, resulting in the reduction of the critical hole density to ~10¹³ cm^-2 when the strain reaches 4% (6%) in SnS₂ (SnSe₂), which can be realized in common field effect transistors. Moreover, the phonon dispersion calculations for the strained SnX₂ monolayers indicate that they can keep the dynamical stability under the hole doping. Therefore, the strain tunable magnetic transition in hole doped tin dichalcogenides indicates their potential promising applications in spintronic devices.