Refining the Spin Hamiltonian in the Spin-1/2 Kagome Lattice Antiferromagnet ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$ using Single Crystals

TL;DR

This study uses single crystal measurements to refine the spin Hamiltonian model of the kagome antiferromagnet ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$, revealing a small easy-axis anisotropy that impacts theoretical interpretations.

Contribution

The paper provides experimental evidence of anisotropic exchange interactions in ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$, refining the theoretical model of its spin Hamiltonian.

Findings

Observed temperature-dependent magnetic susceptibility anisotropy.

Identified small easy-axis exchange anisotropy as a key perturbation.

Results influence theoretical modeling of kagome antiferromagnets.

Abstract

We report thermodynamic measurements of the S=1/2 kagome lattice antiferromagnet ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$, a promising candidate system with a spin-liquid ground state. Using single crystal samples, the magnetic susceptibility both perpendicular and parallel to the kagome plane has been measured. A small, temperature-dependent anisotropy has been observed, where $\chi_{z}/ \chi_{p} > 1$ at high temperatures and $\chi_{z}/ \chi_{p} < 1$ at low temperatures. Fits of the high-temperature data to a Curie-Weiss model also reveal an anisotropy. By comparing with theoretical calculations, the presence of a small easy-axis exchange anisotropy can be deduced as the primary perturbation to the dominant Heisenberg nearest neighbor interaction. These results have great bearing on the interpretation of theoretical calculations based on the kagome Heisenberg antiferromagnet model to the experiments on ZnCu$_{3}$(OH)$_{6}$Cl$_{2}$.