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.