One-dimensional Ising chain with generalized molecular field

The behavior of a spin-$\text{1}\text{2}$ one-dimensional nearest-neighbor Ising chain coupled to a generalized internal molecular field is considered. The internal field is shown to be equivalent to long-range spin-spin interactions. An assumed expansion of the internal field in powers of the magnetization results in the possibility of first- or second-order phase transitions and softening in the spontaneous magnetization and specific heat near the transition temperature. The internal energy and magnetic susceptibility are also discussed.