Partially disordered states of mixed-spin axial next-nearest-neighbor Ising model

Abstract We analyze the nature of the three-dimensional axial next-nearest-neighbor Ising model composed of two kinds (spin-1 and 1 2 ) of alternately stacked ferromagnetic layers by means of the site-dependent molecular-field approximation. Finite-temperature magnetic phase diagram of this model shows the existence of not only partially disordered states in the commensurate modulated phase but also a cusp on the phase boundary between ordered and disordered phases.