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

TL;DR

This study uses Monte Carlo simulations to analyze phase transitions in ultrathin magnetic films modeled by an anisotropic Heisenberg model with long-range interactions, revealing a Berezinskii-Kosterlitz-Thouless transition.

Contribution

It provides the first detailed Monte Carlo analysis supporting the BKT nature of the phase boundary between phases II and III.

Findings

The phase boundary between phases II and III is of BKT type.

The phase diagram includes three distinct phases: ferromagnetic, a mixed phase, and paramagnetic.

Monte Carlo results confirm the order of phase transitions as previously hypothesized.

Abstract

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.