Spin-Coupling Topology in the Copper Hexamer Compounds A$_2$Cu$_3$O(SO$_4$)$_3$ (A=Na, K)

TL;DR

This study investigates copper hexamer compounds with antiferromagnetic order, revealing unique spin-coupling topologies through inelastic neutron scattering and model calculations, advancing understanding of quantum spin systems.

Contribution

The paper introduces a detailed analysis of spin-coupling topology in copper hexamers using neutron scattering and theoretical modeling, highlighting unusual selection rules and magnetic excitation behaviors.

Findings

Unusual selection rules govern magnetic transitions.

Model calculations clarify spin-coupling parameters.

Copper hexamers exhibit S=1 triplet ground states.

Abstract

The compounds A$_2$Cu$_3$O(SO$_4$)$_3$ (A=Na, K) are characterized by copper hexamers which are weakly coupled to realize antiferromagnetic order below TN=3 K. They constitute novel quantum spin systems with S=1 triplet ground-states. We investigated the energy-level splittings of the copper hexamers by inelastic neutron scattering experiments covering the entire range of the magnetic excitation spectra. The observed transitions are governed by very unusual selection rules which we ascribe to the underlying spin-coupling topology. This is rationalized by model calculations which allow an unambiguous interpretation of the magnetic excitations concerning both the peak assignments and the nature of the spin-coupling parameters.