2-DIMENSIONAL QUADRATIC ISING FERROMAGNET WITH APPARENT 3 SPIN INTERACTIONS

For a spin one-half Ising ferromagnet with two-dimensional quadratic lattice, the effects of the apparent three spin interaction, which is reduced effectively to the bilinear exchange interaction between next nearest neighbors, on the Curie temperature, magnetization and the magnetic specific heat have been calculated with the use of Bethe-Peierls theory. The ferromagnetic order is shown to become unstable when the ratio of the three spin interaction to the bilinear exchange interaction amounts to -1/3. Also it is pointed out that the three spin interaction gives significant changes on the Curie temperature and on the temperature dependences of the magnetization and the magnetic specific heat. © 1979, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.