Short-range order in A B3 binary alloy thin films

The theory of order-disorder phenomena in binary alloy thin films of A B3 type is considered in the context of long-range and short-range order parameters. The paper is based on the model introduced in connection with the surface melting and surface disordering considerations in the approach to the samples with the restricted dimension when it requires the construction of a thermodynamically inhomogeneous system consisting of homogeneous subsystems whose entropy determination needs then the pair entropy approximation. Among others, two effects seem to be of particularly great interest: namely, the crossover of the site occupancy in the surface layer and the shift of atoms in the surface plane between two kinds of lattice sites. These effects influence the diffuse low-energy electron diffraction, surface melting, or spin-wave resonance conditions.