The site-diluted spin-1/2 Ising film

The phase transitions of a diluted spin-1/2 Ising film are examined using t he framework of the effective field theory with a probability distribution technique that accounts for the single-site spin correlations. The critical temperature T-c/J of the system is calculated as a function of the thickne ss of the film, the concentration c of magnetic atoms and the ratio R = J(s )/J of the surface constant couplings to the bulk ones. It is shown that fo r R = J(s)/J less than a critical value R,, the critical temperature of the film T-c/J is smaller than the bulk critical temperature T-c(B)/J and for R greater than or equal to R-c, T-c/J is larger than the bulk T-c(B)/J and surface T-c(S)/J critical temperatures of the corresponding semi-infinite s ystem and as the film thickness L is increased further, for R less than or equal to R-c (R greater than or equal to R-c), T-c/J increases (decreases) and approaches asymptotically for large values of L the bulk critical tempe rature T-c(B)/J (the surface critical temperature T-c(S)/J) of the correspo nding semi-infinite system. (C) 1999 Elsevier Science B.V. All rights reser ved.