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 VX (2) (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 VX (2) is larger than that of the single-layer VX (2). 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 Neel temperature (T (N)) of double-layer VX (2) are higher than that of single-layer. As the stress increases, the T (N) 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 VX (2) by stress, and the single-layer and double-layer VX (2) may have potential applications in nano spintronic devices.