Ising nematic phase in ultra-thin magnetic films: a Monte Carlo study

TL;DR

This study uses Monte Carlo simulations to explore the phase transitions in a 2D Ising model with competing interactions, revealing complex critical behavior and the possibility of metastable nematic states in ultra-thin magnetic films.

Contribution

It provides detailed numerical evidence of phase transition scenarios and critical behavior in a model relevant to ultra-thin magnetic films, extending previous theoretical predictions.

Findings

Identification of single first order stripe-tetragonal transition

Discovery of an intermediate Ising nematic phase

Observation of metastable supercooled nematic states

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. We present numerical evidence showing that two different scenarios appear in the model for different values of the exchange to dipolar intensities ratio, namely, a single first order stripe - tetragonal phase transition or two phase transitions at different temperatures with an intermediate Ising nematic phase between the stripe and the tetragonal ones. Our results are very similar to those predicted by Abanov et al [Phys. Rev. B 51, 1023 (1995)], but suggest a much more complex critical behavior than the predicted by those authors for both the stripe-nematic and the nematic-tetragonal phase transitions. We also show that the presence of diverging free energy barriers at the stripe-nematic transition makes possible to obtain by slow cooling a metastable supercooled nematic state down to temperatures well below the transition one.