Long-range magnetic order and interchain interactions in the $S=2$ chain system MnCl$_3$(bpy)

TL;DR

This study investigates the magnetic properties of MnCl₃(bpy), revealing weak interchain interactions, significant Dzaloshinskii-Moriya effects, and strong intrachain coupling, which influence its magnetic order and excitation spectrum.

Contribution

It provides a detailed analysis of the magnetic interactions and excitation spectrum of MnCl₃(bpy), highlighting the role of Dzaloshinskii-Moriya interaction and stronger intrachain coupling than previously known.

Findings

Interchain coupling is very small but Dzaloshinskii-Moriya interaction is substantial.

The intrachain antiferromagnetic interaction is 3.3 meV, stronger than previously reported.

The excitation spectrum is well-described by a 1/S expansion.

Abstract

A compound with very weakly interacting chains, MnCl$_3$(bpy), has attracted a great deal of attention as a possible $S=2$ Haldane chain. However, long-range magnetic order of the chains prevents the Haldane gap from developing below 11.5~K. Based on a four-sublattice model, a description of the antiferromagnetic resonance (AFMR) spectrum up to frequencies of 1.5~THz and magnetic fields up to 50~T indicates that the interchain coupling is indeed quite small but that the Dzaloshinskii-Moriya interaction produced by broken inversion symmetry is substantial (0.12~meV). In addition, the antiferromagnetic, nearest-neighbor interaction within each chain (3.3~meV) is significantly stronger than previously reported. The excitation spectrum of this $S=2$ compound is well-described by a $1/S$ expansion about the classical limit.