Intrinsic magnetism and biaxial strain tuning in two-dimensional metal halides V3X8 (X = F, Cl, Br, I) from first principles and Monte Carlo simulation

Abstract

A novel family of two-dimensional (2D) crystalline metal superhalogens V₃X₈ (X = F, Cl, Br, I) with intrinsic magnetism was predicted using first-principles calculations in the framework of density functional theory (DFT). The calculation results show that the V₃Cl₈ monolayer is an intrinsic anti-ferromagnetic semiconductor (AFS) with an indirect bandgap of 0.086 eV at the PBE functional level, while the V₃X₈ (X = F, Br, I) monolayer exhibits a fascinating ferromagnetic half-metal (FH) property with 100% spin-polarization at the Fermi level. Such 2D materials possess robust dynamical stability as well as thermal stability at room temperature except for V₃Br₈. In addition, Monte Carlo simulations based on the Ising model with the classical Heisenberg model estimate a Curie temperature of approximately 77 K and 103 K for the V₃F₈ and V₃I₈ systems, respectively. Furthermore, we predict an extraordinary phenomenon induced by biaxial compressive strain from the ferromagnetic half-metal (FH) to the ferromagnetic semiconductor (FS) at 2% strain and then to the antiferromagnetic metal (AM) with the biaxial strain increasing up to about 6.3% in the 2D V₃I₈ monolayer. In the case of 2D V₃F₈, as the strain varies from −10% to 8%, a series of electronic and magnetic phase transitions of AFS–AM–FH–AFS will occur. These tunable magnetic and electronic properties of 2D halides originate from the competition between AFM direct nearest-neighbor d–d exchange and FM superexchange via halogen p states, which leads to a variety of magnetic states. The explored controllable magnetic properties, electronic properties and the high Curie temperature render the 2D V₃I₈ monolayer a promising candidate for applications in magnetic logic devices and strain sensor devices.