Phase diagram of an Ising model for ultrathin magnetic films

TL;DR

This paper investigates the phase diagram of a 2D Ising model with competing interactions, revealing new nematic phases and metastable states in ultrathin magnetic films through mean field and Monte Carlo methods.

Contribution

It provides a detailed $( ext{}\delta,T)$ phase diagram analysis, identifying a nematic phase and comparing mean field and Monte Carlo results for ultrathin magnetic films.

Findings

Identification of a nematic phase in the phase diagram.

Discrepancy between mean field and Monte Carlo predictions on stripe width.

Increase in metastable striped states with higher $ ext{ }\delta$.

Abstract

We study the critical properties of a two--dimensional Ising model with competing ferromagnetic exchange and dipolar interactions, which models an ultra-thin magnetic film with high out--of--plane anisotropy in the monolayer limit. In this work we present a detailed calculation of the $(\delta,T)$ phase diagram, $\delta$ being the ratio between exchange and dipolar interactions intensities. We compare the results of both mean field approximation and Monte Carlo numerical simulations in the region of low values of $\delta$, identifying the presence of a recently detected phase with nematic order in different parts of the phase diagram, besides the well known striped and tetragonal liquid phases. A remarkable qualitative difference between both calculations is the absence, in this region of the Monte Carlo phase diagram, of the temperature dependency of the equilibrium stripe width predicted by the mean field approximation. We also detected the presence of an increasing number of metastable striped states as the value of $\delta$ increases.