Is solid copper oxalate a spin chain or a mixture of entangled spin pairs?

TL;DR

This study uses advanced calculations to clarify whether solid copper oxalate behaves as a spin chain or a collection of entangled spin pairs, ultimately confirming its infinite spin-chain nature.

Contribution

The paper applies high-level ab initio calculations to validate the Heisenberg model and interpret magnetic data, resolving long-standing ambiguity about copper oxalate's magnetic structure.

Findings

Supports the infinite spin-chain behavior of copper oxalate

Provides unambiguous interpretation of magnetic susceptibility data

Validates the nearest-site Heisenberg model for this compound

Abstract

Macroscopic assemblies of interacting spins give rise to a broad spectrum of behaviors determined by the spatial arrangement of the magnetic sites and the electronic interactions between them. Compounds of copper (II), in which each copper carries spin $\frac{1}{2}$, exhibit a vast variety of physical properties. For antiferromagnetically coupled spin sites, there are two limiting scenarios: spin chains in which the spins can exhibit a long-range order or a mixture of dimers in which the spins within each pair are entangled but do not communicate with the spins from other dimers. In principle, the two types can be distinguished on the basis of experimental observations and modeling using empirically parameterized effective Hamiltonians, but in practice, ambiguity may persist for decades, as is the case for copper oxalate. Here we use high-level ab initio calculations to establish the validity of the nearest-site Heisenberg model and to predict the interaction strength between the magnetic sites. The computed magnetic susceptibility provides an unambiguous interpretation of magnetic experiments performed throughout half a century, clearly supporting the infinite spin-chain behavior of solid copper oxalate.