Order-disorder layering transitions of a spin-1 Ising model in a variable crystal field

Abstract

The magnetic order-disorder layering transitions of a spin-1 Ising model are investigated, under the effect of a variable surface crystal field ${\Delta }_s$, using the mean field theory. Each layer $k$, of the film formed with $N$ layers, disorders at a finite surface crystal field distributed according to the law ${\Delta }_k={\Delta }_s/k^{\alpha }$, $k=1,2,...,N$ and $\alpha$ being a positive constant. We have established the temperature-crystal field phase diagrams and found a constant tricritical point and a reentrant phenomenon for the first $k_0$ layers. This reentrant phenomenon is absent for the remaining $N-k_0$ layers, but the tricritical points subsist and depend not only on the film thickness but also on the exponent $\alpha$. On the other hand, the thermal behaviour of the surface magnetisation for a fixed value of the surface crystal field ${\Delta }_s$ and selected values of the parameter $\alpha$ are established.

10 Pages Latex, 9 Figures Postscript. To appear in JMMM (2002)

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