Surface effects of ordering in binary alloys

This article reviews the most important achievements in the studies of the compositional (chemical) and magnetic ordering effects in the surface region of single-crystal binary alloys with different bulk structures. These alloys include the non-magnetic and magnetic concentrated substitutional binary systems which have a tendency to ordering (Au–Cu, Cu–Pt, Fe–Pt, Co–Fe, Fe–Ni, Al–Fe, Al–Ni, Pt–Ti, Cu–Pd, Co–Pt, Ni–Pt, Al–Cu, Cu–Al). A number of analytical methods very sensitive to the surface region have been recently developed to obtain a more detailed knowledge of the crystallographic symmetry and lattice parameters, and these as well as compositional and spin order parameters of the outermost few atom layers of alloys are briefly described. Of primary interest are the following phenomena observed from the experimental studies of the various ordering alloys: the face-dependent bulk termination; surface composition and surface segregation oscillatory profile; face-related ‘sandwich’ segregation; strong surface multilayer and rippled relaxation as well as buckling in the first few layers; surface reconstruction and formation of the surface superstructure; the temperature-dependent surface compositional and magnetic order parameters; kinetics of the order–disorder phase transition; surface electron structure; surface ferromagnetic anomalies. After a review of the experimental data the interplay between theory and experiment is also discussed. This comparison has proved particularly useful for understanding the nature of the surface ordering effects in alloys.