This award will support a U.S.-Mexico scientific collaboration between Professor Juan Sanchez of the the University of Texas, Austin and Professors J. L. Moran Lopez and F. Mejia Lira of the Physics Department of the University of San Luis de Potosi, Mexico. The purpose of this collaboration is the characterization of magnetic interactions and of planar defects, such as surfaces, on alloy phase stability. Several real and model alloy systems will be investigated using the cluster variation method of statistical mechanics, from which accurate configurational free energies may be calculated. The collaboration builds on previously successful efforts initiated over five years ago working on alloy phase stability. As a result of these prior efforts, the researchers have identified the following areas of common interest and mutual benefit: phase equilibrium in magnetic alloys; surface phenomena in close-packed structures; ordering phenomena in superconducting ceramics; and thermodynamics of small metallic clusters.