Electronic and magnetic properties of single-layer and double-layer VX 2 (X = Cl, Br) under biaxial stress*

First-principles calculations and Monte Carlo simulations reveal that single-layer and double-layer VX2 (X=Cl,Br) can be tuned from antiferromagnetic (AFM) semiconductors to ferromagnetic (FM) state when biaxial tensile stress is applied. Their ground states are all T phase. The biaxial tensile stress at the phase transition point of the double-layer VX2 is larger than that of the single-layer VX2. The direct band gaps can be also manipulated by biaxial tensile stress as they increases with increasing tensile stress to a critical point and then decreases. The Néel temperature (TN) of double-layer VX2 are higher than that of single-layer. As the stress increases, the TN of all materials tend to increase. The magnetic moment increases with the increase of biaxial tensile stress, and which become insensitive to stress after the phase transition points. Our research provides a method to control the electronic and magnetic properties of VX2 by stress, and the single-layer and double-layer VX2 may have potential applications in nano spintronic devices.