Anisotropic melting of frustrated Ising antiferromagnets

TL;DR

This study reveals that in frustrated 2D Ising antiferromagnets, magnetic order melts through an intermediate anisotropic correlated phase before becoming isotropic, with the intermediate phase's width increasing with frustration.

Contribution

It uncovers a two-stage melting process involving an anisotropic correlated phase and an exotic incommensurate liquid-like phase in frustrated Ising models.

Findings

Intermediate anisotropic correlated phase exists between T_N and T*

Incommensurate liquid-like phase with algebraic correlations forms in 2D

Width of the intermediate phase increases with frustration

Abstract

Magnetic frustrations and dimensionality play an important role in determining the nature of the magnetic long-range order and how it melts at temperatures above the ordering transition $T_N$. In this work, we use large-scale Monte Carlo simulations to study these phenomena in a class of frustrated Ising spin models in two spatial dimensions. We find that the melting of the magnetic long-range order into an isotropic gas-like paramagnet proceeds via an intermediate stage where the classical spins remain anisotropically correlated. This correlated paramagnet exists in a temperature range $T_N < T < T^\ast$, whose width increases as magnetic frustrations grow. This intermediate phase is typically characterized by short-range correlations, however the two-dimensional nature of the model allows for an additional exotic feature -- formation of an incommensurate liquid-like phase with algebraically decaying spin correlations. The two-stage melting of magnetic order is generic and pertinent to many frustrated quasi-2D magnets with large (essentially classical) spins.