Strain-tunable electric structure and magnetic anisotropy in monolayer CrSI

Two-dimensional (2D) ferromagnetic semiconductors provide platforms for studying novel physical phenomena in low dimensional materials. Using first-principles calculations, we systematically investigate the effect of strain on the electronic structure and magnetic anisotropy energy (MAE) of monolayer CrSI. The results demonstrate that the easy axis of unstrained monolayer CrSI is parallel to the in-plane [100] axis and the MAE of monolayer CrSI is mainly contributed by the spin-polarized p-orbitals of nonmetallic I atoms. Remarkably, the strain transforms the ground state of monolayer CrSI from a ferromagnetic semiconductor to ferromagnetic metal. More importantly, the external strain can switch the direction of the easy axis of monolayer CrSI and compressive strain significantly enhances the MAE of the I atom to reach 0.52 meV per atom, which is comparable to that of metallic Fe atoms at Fe/MgO interfaces. Furthermore, we elucidate that the increase of the positive contributions of matrix element differences between the spin-up p(x) and p(y) orbitals as well as spin-up p(y) and p(z) orbitals of the I atom to MAE with respect to compressive strain is the main cause of the significant enhancement in perpendicular magnetic anisotropy of monolayer CrSI under -10% compressive strain. Our research proves that monolayer CrSI has a good application prospect in magnetic storage devices.