Wetting and layering transitions in magnetic films

Abstract

The understanding of the surface effect on wetting and layering transitions was explained both theoretically and experimentally. Indeed, using different spin system models and different numerical and approximate methods such as mean field and effective field theories, real space renormalization technique and Monte-Carlo simulations, it is found that the wetting and layering transitions depend on the nature of the surface magnetic field, the surface coupling strength, the surface crystal field, the geometry of surface, the in-homogeneity of substrate and the quantum fluctuations at the surface. It is also found that the layering transition temperature increases or decreases as a function of the film thickness depending on the surface coupling values. The wetting transition temperature can be greater or smaller than the layering temperature. In the case of a variable surface crystal field, an order-disorder layering reentrance is found with new critical exponents behaviour. The wetting phenomena are also influenced by the nature of the surface. In fact the intra-layer transitions appear under the effect of an edge on the surface and/or corrugated surfaces. However, the intra-layering transitions are found for a surface temperature above, which the surface and the intra-layer surface occur. While the bulk layering and intra-layering transitions appear above another finite temperature which is greater than the former one. Such result is not found in the case of a perfect surface. Beside this, and under the corrugation effect, the pre-wetting phenomena and layering transitions occur at zero temperature, even in the case of a uniform magnetic field. In this case the wetting temperature depends strongly on the width of the corrugated-steps but weakly on its number.

Study of Critical Behaviour in Diluted Ferromagnetic: Thin Films and Semi-Infinites Films

“…For R 2 < R C 2 , τ C is less than the bulk critical temperature τ B C and approaches the last one for large values of L. For R 2 > R C 2 , the system orders at the surfaces before it does in the bulk and approaches a limit dependent on the surface exchange coupling that corresponds to the surface magnetic transition observed in the corresponding semiinfinite film. [23][24][25][26]75 These are the general qualitative results for the ferromagnetic thin films that have been obtained in other approximate methods, [23][24][25][26]74,76 but with a different value of R C 2 , which may be due to the consideration of the spinspin correlations. We have also studied the influence of exchange coupling of the behaviours the effective the critical exponents γ(ν) and ν b in the thin film for two structures.…”

“…One may explain this feature as follows: for R 2 > R C 2 , the system may order at the surface magnetism dominates and when the number of layers is very large, the critical temperature approaches a value, dependent on the surface exchange coupling, that corresponds to the surface magnetic transition observed in the corresponding semi-infinite film. [23][24][25][26]65 The effect of surface is particularly strong when the film thickness becomes small and leads a possible competition between magnetism at surface and in the bulk. This may induced the appearance of a maximum for R 2 < R C 2 and for small thickness.…”

“…The phase transition of a diluted Ising film using the effective field theory that account for the single-site spin correlations has been studied by Saber. [23][24][25][26] Lin et al 27 have developed an analytical method based on the variational cumulant expansion to calculate the critical temperature of the Ising film as a function of the film thickness. The semi-infinite Ising film with surface amorphization has been studied by Kaneyoshi 28 using the effective field theory and by Ilkovic 29 with the aid of reaction mean-field theory.…”

Critical adsorption at chemically structured substrates

“…On chem-ically structured substrates mostly wetting experiments have been performed [27,28,29]. The present paper extends theoretical work on critical adsorption on chemically homogeneous [30,31,32,33] and topologically [34] structured surfaces and work on wetting phenomena at chemically structured substrates [35,36,37,38,39] to the case of critical adsorption on geometrically flat, but chemically structured surfaces.…”