Magnetic Properties of an Ising Spin System with Two-Spin and Four-Spin Interactions

The magnetic properties of the Ising spin (S=1/2 and 1) system with a bilinear exchange interaction J0SizSjz, and a four-site four-spin interaction JSizSjzSkzSlz, are discussed by making use of Monte Carlo (MC) simulations of the magnetization and magnetic specific heat. Especially at a certain interaction ratio J/J0, e.g. for the square lattice at the condition |J/J0| = 2 and 1/2 for S = 1/2 and 1, respectively, the thermal average SizSjzSkzSlz > align=middle border=0 > shows a characteristic temperature dependence in the low temperature region and becomes an essential parameter to detect the phase change of the present system.