Infinitely Many Commensurate Phases in a Simple Ising Model

On the basis of systematic low-temperature expansions "to all orders", it is shown that an infinite sequence of spatially modulated commensurate phases, with wave vectors πj(2j+1)a (j=0, 1, 2,), occurs in simple, anisotropic Ising models with nn couplings J₀, J₁>0, in between spin-{} layers, and competing nnn interlayer couplings J₂=-kJ₁ along one axis. The free energies, interfacial tensions, and phase boundaries are found for low T in $d>2$ dimensions.