Magnetic Susceptibility of Collinear and Noncollinear Heisenberg Antiferromagnets

TL;DR

This paper develops a molecular field theory calculation for magnetic susceptibility in various collinear and noncollinear Heisenberg antiferromagnets, matching experimental data without adjustable parameters and clarifying universal behaviors.

Contribution

It presents a new MFT approach for chi(T<=TN) applicable to diverse AFMs without magnetic sublattices, extending previous limited models.

Findings

The theory fits experimental susceptibility data well.

Quantifies deviations due to spin correlations and fluctuations.

Clarifies the universal susceptibility behavior in triangular lattice AFMs.

Abstract

Predictions of the anisotropic magnetic susceptibility chi below the antiferromagnetic (AFM) ordering temperatures TN of local moment Heisenberg AFMs have been made previously using molecular field theory (MFT) but are very limited in their applicability. Here a MFT calculation of chi(T<=TN) is presented for a wide variety of collinear and noncollinear Heisenberg AFMs containing identical crystallographically equivalent spins without recourse to magnetic sublattices. The results are expressed in terms of directly measurable experimental parameters and are fitted with no adjustable parameters to experimental chi(T<=TN) data from the literature for several collinear and noncollinear AFMs. The influence of spin correlations and fluctuations beyond MFT is quantified by the deviation of the theory from the data. The origin of the universal chi(T<=TN) observed for triangular lattice AFMs exhibiting coplanar noncollinear 120 degree AFM ordering is clarified.