Specific heat of quasi-2D antiferromagnetic Heisenberg models with varying inter-planar couplings

TL;DR

This study uses quantum Monte Carlo simulations to analyze how varying inter-layer couplings affect the specific heat and phase transition features in 3D antiferromagnetic Heisenberg models, revealing a separation of thermal peaks.

Contribution

It provides a detailed separation of intra- and inter-layer contributions to specific heat, elucidating the effects of weak inter-plane couplings on 3D ordering peaks in quasi-2D antiferromagnets.

Findings

The 3D ordering peak height decreases linearly with decreasing inter-plane coupling.

A clear separation exists between the 2D short-range order maximum and the 3D transition peak.

Results help explain the absence of specific heat anomalies in some quasi-2D antiferromagnets.

Abstract

We have used the stochastic series expansion (SSE) quantum Monte Carlo (QMC) method to study the three-dimensional (3D) antiferromagnetic Heisenberg model on cubic lattices with in-plane coupling J and varying inter-plane coupling J_perp < J. The specific heat curves exhibit a 3D ordering peak as well as a broad maximum arising from short-range 2D order. For J_perp << J, there is a clear separation of the two peaks. In the simulations, the contributions to the total specific heat from the ordering across and within the layers can be separated, and this enables us to study in detail the 3D peak around T_c (which otherwise typically is dominated by statistical noise). We find that the peak height decreases with decreasing J_perp, becoming nearly linear below J_perp = 0.2J. The relevance of these results to the lack of observed specific heat anomaly at the ordering transition of some quasi-2D antiferromagnets is discussed.