Partially Disordered Phases of the Axial Next-Nearest-Neighbor Ising Model with Alternating Intra- and Inter-layer Interactions

We study a new axial next-nearest-neighbor Ising (ANNNI) model in which both the strength of intralayer and interlayer interactions alternate along the c-axis, respectively. The results of a site-dependent mean-field approximation show that the alternation of these interactions causes the partially disordered phase (PDP) and a crossing behavior between two PDPs of and where (or ) means a layer magnetized along (or ) direction and means a paramagnetic layer. In an extremely low temperature region around the multi-phase point, we found the reentrant phase transition producing the successive phase transitions - > with increasing temperature.