CONICET | Buscador de Institutos y Recursos Humanos

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. Byproperly choosing the crystal field (D), which regulates the density of nonmagnetic species (S = 0), such thatthose impurities are excluded from the bulk (where D = −∞) except in the middle of the sample [whereDM (L/2) = −∞], we are able to control the presence of a defect line in the middle of the sample and studyits influence on the interface between domains of different spin orientations. So essentially we study an Isingmodel with a defect line but, unlike previous work where defect lines in Ising models were defined via weakenedbonds, in the present case the defect line is due to mobile vacancies and hence involves additional entropy. Inthis way, by drawing phase diagrams, i.e., plots of the wetting critical temperature (Tw ) versus the magnitude ofthe crystal field at the middle of the sample (DM ), we observe curves of (first-) second-order wetting transitionstctcfor (small) high values of DM . Theses lines meet in tricritical wetting points, i.e., (Tw ,DM ), which also dependon the magnitude of the surface magnetic fields. It is found that second-order wetting transitions satisfy thescaling theory for short-range interactions, while first-order ones do not exhibit hysteresis, provided that smallsamples 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 jumpof the order parameter in small samples