Phase diagrams of site diluted ferromagnetic thin film

Abstract

The phase transition properties of Ising, classical XY and Heisenberg of diluted ferromagnetic thin film are studied by the method of exact high-temperature series expansions extrapolated with the Padé approximants method. The reduced critical temperature τ c of the diluted ferromagnetic thin films is studied as a function of film thickness L and the exchange interactions in the bulk J b , in the surface J s and between surface and nearest-neighbour layer J ⊥ . It is found that τ c increases with the exchange interactions of surface and L. The magnetic phase diagram ( τ c versus dilution x) is obtained. A critical value of the surface exchange interaction above which the surface magnetism appears is obtained. The dependence of the critical parameter of surface reduced coupling R 2 c as a function of the dilution x and the ratio of the exchange interaction between the surface and nearest-neighbour layer to the bulk one R 1 for the three studied models has been investigated. The percolation threshold is defined as the concentration x p at which τ c = 0 . The obtained values are x p ≈ 0.2 in the bulk and x p ≈ 0.4 at the surface.