Role of Second-Neighbor Interaction in Diluted Ferromagnetic Systems

Abstract

The Ising spin systems with first- and second-neighbor interactions are studied by applying the cluster theory proposed by one of the authors (H. Mano). The role of the second-neighbor interaction in pure and diluted ferromagnets is discussed by calculating over-all magnetic properties such as specific heat and spontaneous magnetization as well as the Curie temperature and the critical concentration. In diluted systems interesting phenomena are found when the second-neighbor interaction is small and ferromagnetic. The curve of the Curie temperature against the concentration of magnetic atoms has a trail near the critical concentration. The specific heat has a new maximum and the spontaneous magnetization shows considerable decrease in the low temperature region well below the transition temperature.