Phase transition in Heisenberg magnetic films

The phase transitions of a ferromagnet spin-S Heisenberg thin film are examined using the high-temperature series expansions technique extrapolated with Padé approximants method. The critical reduced temperature of the system τc=kBTc/2S(S+1)Jb is studied as function of the thickness of the film and the exchange interactions in the bulk, and within the surfaces Jb, Js and J⊥, respectively. A critical value of surface exchange interaction above which the surface magnetism appears is obtained. The dependence of the reduced critical temperature on the film thickness L has been investigated. The effects of an amorphous magnetic surface on the critical properties of the film have been studied. The results show that the magnetic order of the thin film may be destroyed by a higher amorphization on the surface layers.