Phase transition in ultrathin magnetic films with long-range interactions: Monte Carlo simulation of the anisotropic Heisenberg model

摘要

Ultrathin magnetic films can be modeled as an anisotropic Heisenberg model with long-range dipolar interactions. It is believed that the phase diagram presents three phases: An ordered ferromagnetic phase (Ⅰ), a phase characterized by a change from out-of-plane to in-plane in the magnetization (Ⅱ), and a high-temperature paramagnetic phase (Ⅲ). It is claimed that the border lines from phase Ⅰ to Ⅲ and Ⅱ to Ⅲ are of second order and from Ⅰ to Ⅱ is first order. In the present work we have performed a very careful Monte Carlo simulation of the model. Our results strongly support that the line separating phases Ⅱ and Ⅲ is of the BKT type.