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RESEARCH PRODUCT

Surface-induced disordering at first-order transitions in body-centered cubic binary alloys: A Monte-Carlo simulation

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Surface effects on the phase transition from theDO3 phase to the disordered phase are studied for a bcc Ising antiferromagnet with nearest and next-nearest neighbor exchange interactions in a magnetic field. This model can also be considered to represent binary alloys such as the FeAl-system; missing interactions near the surface translate then into surface magnetic fields. The change of the local magnetization near the surface then corresponds to “surface enrichment” of one component. For a plausible choice of parameters surface-induced disordering is found and the associated critical behavior is studied. Varying the bulk fieldH near the transition fieldHc, we find that the thickness of the disordered layer increases proportional to ln(H-Hc) while the local order parameter at the surface vanishes as (H-Hc)1/2. These results are consistent with mean field predictions for the single order parameter case, although several “ordering fields” occur (sublattice magnetizations and magnetization).