Quasi-reentrant interface behavior of two-dimensional frustrated Ising models

For a two-dimensional frustrated Union Jack Ising model, we give exact calculations of anisotropic interface tension, equilibrium crystal shape (ECS), squared scaled interface width and interface entropy by an extended Feynman-Vdovichenko's random walk method. In addition to the region where the reentrant phase transition occurs, we find a wide area of the quasi-reentrant region where an interface entropy is negative and ECS extends with increasing temperature.