Rough interfaces in a bcc-based binary alloy

The structure of antiphase domain boundaries in the ordered phase of body-centered-cubic alloys is investigated by Monte Carlo simulations, studying a fairly realistic model of iron-aluminum alloys that includes a description of the magnetic properties of iron within a nearest-neighbor Heisenberg Hamiltonian. An interface is enforced by employing in one lattice direction an odd number of lattice planes and choosing periodic boundary conditions throughout. At the temperatures of interest, the antiphase domain boundary is not localized in the system and is rough, which implies a logarithmic dependence of the interfacial width on the linear dimension ${\mathit{L}}_{\mathrm{\ensuremath{\parallel}}}$ parallel to the interface. Methods are introduced to define an instantaneous interface position for each configuration that is analyzed. Choosing a coordinate frame whose origin is fixed at this (moving) interface position, profiles of order parameter, concentration, etc., can be estimated. It is found that capillary wave theory accounts for the interface widths reasonably well. Near the bulk critical temperature the lengths characterizing the intrinsic interfacial widths agree with the bulk correlation length, which is obtained from an independent investigation of correlation functions in the bulk. Finally, the interfacial enrichment of the majority species in the domain wall is studied and it is shown that the critical behavior of the interfacial excess concentration is consistent with scaling predictions.