Magnetic properties of a transverse spin-1/2 Ising film

Within the framework of the effective-held theory, we examine the phase tra nsitions of a transverse spin-1/2 Ising film. The critical temperatures of the film as a function of the interactions, transverse fields, and film thi ckness are studied. It is found that for the ratio of the surface interacti ons to the bulk ones R = J(s)/J less than a critical value R-c, the critica l temperature T-c/J of the film is smaller than the bulk critical temperatu re T-C(B)/J and as the film thickness L is increased further, T-c/J increas es and approaches asymptotically T-C(B)/J for large values of L. However, f or R > R-c, T-c/J is larger both than the bulk T-C(B)/J and the surface T-C (S)/J critical temperatures of the corresponding semi-infinite system and a s the film thickness L is increased further, T-c/J decreases and approaches asymptotically, for large values of L, the surface magnetic transition T-C (S)/J observed in the corresponding semi-infinite system. We calculate also some magnetic properties of the film such as the layer magnetizations, the ir averages and their profiles and the longitudinal susceptibility of the f ilm. The film longitudinal susceptibility still diverges at the film critic al temperature as does the bulk longitudinal susceptibility, but its magnit ude is reduced. Also there is a rounded peak at the bulk critical temperatu re when R > R-c. The bulk related character of the susceptibility is more p ronounced and the surface related character is less pronounced when the fil m thickness is large. [S0163-1829(99)03706-6].