A ug 2 00 5 Interface disorder and layer transitions in Ising thin films

The disorder and layer transitions in the interface between an Ising spin-1/2 film denoted (n), and an Ising spin-1 film denoted (m), are studied using Monte Carlo simulations. The effects of both an external magnetic field, acting only on the spin-1/2 film , and a crystal magnetic field acting only on the spin-1 film, are studied for a fixed temperature and selected values of the coupling constant J p between the two films. It is found that for large values of the constant J p , the layers of the film (n), as well as those of the film (m), undergo a first order layering transition. On the other hand, the only disordered layer of the film (n) is that one belonging to the interface films (n)/(m), for any values of the crystal field ∆. We show the existence of a critical value of the crystal field ∆ c , above which this particular layer of the film (n) is disordered. We found that ∆ c depends on the values of the constant coupling J p between the two films.