Tunable Magnetic Coupling of Monolayer CrI2by Strain Engineering

We report a first-principles study of magnetic properties of a monolayer CrI2 under external strain. Our results reveal that an intrinsic CrI2 monolayer is antiferromagnetic (AFM) in its ground state. However, applying strain destabilizes this magnetic order, leading to a phase transition. Specifically, biaxial tensile strain above 2% or uniaxial strain along the a-axis exceeding 4% induces a transition from the AFM to the ferromagnetic (FM) state. This behavior arises from competing magnetic interactions of direct nearest-neighbor interaction and d-p-d superexchange interactions mediated by iodine p-orbitals. Our analysis highlights the dominant FM first-nearestneighbor exchange (J1 > 0) and its AFM-FM transition through modulation of the second-nearest-neighbor exchange (J2). We discuss the mechanism of the superexchange interaction based on the Goodenough-Kanamori rule and Anderson's mechanism to clarify the origin of the magnetic phase transition. These findings highlight the potential of strain engineering to modulate magnetic coupling in CrI2, making it a promising candidate for future nanospintronics applications.