Biaxial strain induced multiple magnetic phase transitions in nonmagnetic transition metal halide monolayer

Two-dimensional (2D) materials are sensitive to external stimuli. In this work, via a combined first-principles simulations and constrained random phase approximation, we report strain-induced multiple magnetic phase transitions in an exfoliable nonmagnetic metallic 2D material ScI2. Interestingly, monolayer ScI2 has a high density of states at the Fermi level [N(E-F)]. Its product with the Stoner parameter is estimated to be slightly below the critical value of the Stoner criterion for spontaneous spin splitting. Moreover, we show bi-axial strains can effectively increase the N(E-F) of ScI2, leading to phase transitions to magnetic states. While the tensile strain first yields an antiferromagnetic state at the critical magnitude of 3%, then a normal ferromagnetic state at 5%, and half-metallicity with large spin flip gaps for the minority spins for strains >= 6%, compressive strain induces a ferromagnetic configuration ranging from -6% to -10%. Our results demonstrate a system with strain controllable magnetic states, appealing for straintronic and spintronic applications, and provide guidance on the design of extrinsic 2D magnetic materials.