A mean-field theory for strongly disordered non-frustrated antiferromagnets

TL;DR

This paper develops a mean-field theory for strongly disordered, non-frustrated antiferromagnets, revealing complex phase transitions and critical points influenced by random magnetic couplings.

Contribution

It introduces a novel mean-field approach that captures the effects of broad coupling distributions in disordered antiferromagnets, predicting split spin-flop transitions and critical phenomena.

Findings

First-order spin-flop transition splits into two at low temperatures.

Existence of bicritical point or critical endpoint in phase diagram.

Enhanced spin-flop signatures at higher temperatures.

Abstract

Motivated by impurity-induced magnetic ordering phenomena in spin-gap materials like TlCuCl3, we develop a mean-field theory for strongly disordered antiferromagnets, designed to capture the broad distribution of coupling constants in the effective model for the impurity degrees of freedom. Based on our results, we argue that in the presence of random magnetic couplings the conventional first-order spin-flop transition of an anisotropic antiferromagnet is split into two transitions at low temperatures, associated with separate order parameters along and perpendicular to the field axis. We demonstrate the existence of either a bicritcal point or a critical endpoint in the temperature-field phase diagram, with the consequence that signatures of the spin flop are more pronounced at elevated temperature.