title: First-order and tricritical wetting transitions in the two-dimensional Ising model caused by interfacial pinning at a defect line.
abstract: We present a study of the critical behavior of the Blume-Capel model with three spin states (S=±1,0) confined between parallel walls separated by a distance L where competitive surface magnetic fields act. By properly choosing the crystal field (D), which regulates the density of nonmagnetic species (S=0), such that those impurities are excluded from the bulk (where D=-∞) except in the middle of the sample [where D(M)(L/2)≠-∞], we are able to control the presence of a defect line in the middle of the sample and study its influence on the interface between domains of different spin orientations. So essentially we study an Ising model with a defect line but, unlike previous work where defect lines in Ising models were defined via weakened bonds, in the present case the defect line is due to mobile vacancies and hence involves additional entropy. In this way, by drawing phase diagrams, i.e., plots of the wetting critical temperature (T(w)) versus the magnitude of the crystal field at the middle of the sample (D(M)), we observe curves of (first-) second-order wetting transitions for (small) high values of D(M). Theses lines meet in tricritical wetting points, i.e., (T(w)(tc),D(M)(tc)), which also depend on the magnitude of the surface magnetic fields. It is found that second-order wetting transitions satisfy the scaling theory for short-range interactions, while first-order ones do not exhibit hysteresis, provided that small samples are used, since fluctuations wash out hysteretic effects. Since hysteresis is observed in large samples, we performed extensive thermodynamic integrations in order to accurately locate the first-order transition points, and a rather good agreement is found by comparing such results with those obtained just by observing the jump of the order parameter in small samples.
authors.affiliation: Instituto de Física de Líquidos y Sistemas Biológicos (IFLYSIB), CCT-CONICET La Plata, UNLP. Calle 59 Nro. 789, (1900) La Plata, Argentina and Facultad de Ingeniería, Universidad Nacional de La Plata, Argentina.
authors.forename: Marta L
authors.initials: ML
authors.lastname: Trobo
authors.affiliation: Instituto de Física de Líquidos y Sistemas Biológicos (IFLYSIB), CCT-CONICET La Plata, UNLP. Calle 59 Nro. 789, (1900) La Plata, Argentina and Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina.
authors.forename: Ezequiel V
authors.initials: EV
authors.lastname: Albano
authors.affiliation: Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudinger Weg 7, D-55099 Mainz, Germany.
authors.forename: Kurt
authors.initials: K
authors.lastname: Binder
mesh_terms: D003198:Computer Simulation; D060526:Magnetic Fields; D008962:Models, Theoretical; D009010:Monte Carlo Method; D044367:Phase Transition; D013816:Thermodynamics; D017155:Wettability