Phase diagram of the Ising model on the square lattice with crossed diagonal bonds

Abstract

The global phase diagram of the spin-1/2 Ising model with nearest- and next-nearest-neighbor interactions on the square lattice is considered, including the fully anisotropic cases. A closed-form expression is given that accurately represents the phase boundaries when the crossed next-nearest-neighbor interactions are not of opposite signs. The phase diagram includes disordered, ferromagnetic, antiferromagnetic, axially single-striped, and diagonally double-striped phases.