Thermodynamics of anisotropic triangular magnets with ferro- and antiferromagnetic exchange

TL;DR

This study uses finite temperature Lanczos method to analyze thermodynamic properties of anisotropic triangular quantum spin systems, revealing asymmetric peak behaviors and providing insights into specific materials like Cs2CuCl4 and Cs2CuBr4.

Contribution

It applies FTLM to large clusters for the first time to study thermodynamics of anisotropic triangular magnets, revealing asymmetric peak behaviors and modeling real materials.

Findings

Peak positions and heights vary asymmetrically in different magnetic phases.

Evidence of potential second maxima or shoulders at lower temperatures.

Explicitly models exchange parameters for Cs2CuCl4 and Cs2CuBr4.

Abstract

We investigate thermodynamic properties like specific heat $c_{V}$ and susceptibility $\chi$ in anisotropic $J_1$-$J_2$ triangular quantum spin systems ($S=1/2$). As a universal tool we apply the finite temperature Lanczos method (FTLM) based on exact diagonalization of finite clusters with periodic boundary conditions. We use clusters up to $N=28$ sites where the thermodynamic limit behavior is already stably reproduced. As a reference we also present the full diagonalization of a small eight-site cluster. After introducing model and method we discuss our main results on $c_V(T)$ and $\chi(T)$. We show the variation of peak position and peak height of these quantities as function of control parameter $J_2/J_1$. We demonstrate that maximum peak positions and heights in N\'eel phase and spiral phases are strongly asymmetric, much more than in the square lattice $J_1$-$J_2$ model. Our results also suggest a tendency to a second side maximum or shoulder formation at lower temperature for certain ranges of the control parameter. We finally explicitly determine the exchange model of the prominent triangular magnets Cs$_2$CuCl$_4$ and Cs$_{2}$CuBr$_{4}$ from our FTLM results.