Phase transitions in surface segregation of ${\mathrm{Pt}}_{\mathit{c}}$${\mathrm{Ni}}_{1\mathrm{-}\mathit{c}}$ alloys from tight-binding Ising-model calculations

The tight-binding Ising model coupled with a mean-field approximation formulated as an area-preserving map is applied to surface segregation of ${\mathrm{Pt}}_{\mathit{c}}$ ${\mathrm{Ni}}_{1\mathrm{-}\mathit{c}}$ alloys. It allows us to reproduce the striking experimental data available for the low-index faces and in particular the face-related segregation reversal observed when going from the (111) to the (110) face. Moreover, it predicts some spectacular phase transitions of the concentration profiles as a function of temperature and bulk concentration.