Neutron scattering from a coordination polymer quantum paramagnet

TL;DR

This study uses inelastic neutron scattering to analyze a quantum paramagnet, revealing its quasi-one-dimensional two-legged spin ladder structure and quantifying exchange interactions.

Contribution

It provides detailed experimental data and theoretical analysis identifying the magnetic structure and exchange parameters of Cu(Quinoxaline)Br2 as a two-legged spin-1/2 ladder.

Findings

Magnetic excitations observed above 1.9 meV energy gap.

Material identified as a two-legged spin-1/2 ladder.

Excellent fit of data with the continuous unitary transformation model.

Abstract

Inelastic neutron scattering measurements are reported for a powder sample of the spin-1/2 quantum paramagnet $\rm Cu(Quinoxaline)Br_2$. Magnetic neutron scattering is identified above an energy gap of 1.9 meV. Analysis of the sharp spectral maximum at the onset indicates that the material is magnetically quasi-one-dimensional. Consideration of the wave vector dependence of the scattering and polymeric structure further identifies the material as a two-legged spin-1/2 ladder. Detailed comparison of the data to various models of magnetism in this material based on the single mode approximation and the continuous unitary transformation are presented. The latter theory provides an excellent account of the data with leg exchange $J_{\parallel}=2.0$ meV and rung exchange $J_{\perp}=3.3$ meV.