Nonlinear Effect on the Axial Next-Nearest Neighbor Ising (ANNNI) Model: Application to CeSb

Abstract

Mean field calculations are made to study the effect of nonlinear terms with respect to the magnetization in the axial next-nearest neighbor Ising (ANNNI) model. The phase diagrams are calculated in both zero and nonzero magnetic fields, in which a large number of high-order commensurate phases is found. It is shown that the nonlinear effect makes the ordered phase stable at higher temperatures and larger fields. Partially disordered states which contain paramagnetic sites are also obtained, resulting from the nonlinear effect as well as the competition between the intralayer coupling and the entropy effect. In this connection, the theory is compared with the complex magnetic phase diagram of CeSb.