To understand the surface and bulk phase transitions, we study a coupled 2-layer Ising ferromagnetic system. We have studied the system by Monte Carlo simulations and mean field calculations. Numerical results show that there exists only one critical temperature as long as the interlayer coupling is not equal to zero. This result is not surprising because an ordered layer will exert an effective field on the other layer through the interlayer coupling. This effective field will cause the other layer to become ordered. Applying the same argument to a semi-infinite layered system, one will expect following results in a semi-infinite layered Ising system: (1) There are two transition temperatures if the ratio of the surface intralayer coupling J_s and the bulk coupling J_b is greater than a...[ Read more ]

To understand the surface and bulk phase transitions, we study a coupled 2-layer Ising ferromagnetic system. We have studied the system by Monte Carlo simulations and mean field calculations. Numerical results show that there exists only one critical temperature as long as the interlayer coupling is not equal to zero. This result is not surprising because an ordered layer will exert an effective field on the other layer through the interlayer coupling. This effective field will cause the other layer to become ordered. Applying the same argument to a semi-infinite layered system, one will expect following results in a semi-infinite layered Ising system: (1) There are two transition temperatures if the ratio of the surface intralayer coupling J_s and the bulk coupling J_b is greater than a certain value ([is greater than] l), one for the surface transition temperature and the other for the bulk. (2) There is only one transition temperature if the ratio is smaller than that value. We have also obtained the interlayer coupling dependence on the critical temperature both numerically and analytically.