Nonlinear Effect on the Axial Next-Nearest Neighbor Ising (ANNNI) Model. II. Application to CeBi

Abstract

Nonlinear terms with respect to the magnetization are added to the free energy of the axial next-nearest neighbor Ising (ANNNI) model. Mean field calculations are made to investigate the phase diagram for both zero and nonzero magnetic fields. It is found that the nonlinear terms give a temperature dependent modification to the coupling constants of the conventional ANNNI model; this effect brings about a new phase transition. The nonlinear effect on the transition line between the ferromagnetic and modulated states under magnetic fields is also studied. A comparison is made between the theory and the phase diagram of CeBi in this context.