Revisiting the chain magnetism in Sr14Cu24O41: Experimental and numerical results

TL;DR

This study combines experimental ESR and magnetization measurements with numerical simulations to analyze the magnetic properties of Sr14Cu24O41, revealing the presence of unpaired Cu spins and validating an effective Heisenberg model.

Contribution

It provides new experimental evidence and numerical modeling that clarify the magnetic ground state and unpaired spins in Sr14Cu24O41, supporting recent ab initio calculations.

Findings

Paramagnetic centers are unpaired Cu spins, not defects.

Magnetization behavior matches an effective Heisenberg model.

Ground state includes dimers, trimers, and monomers.

Abstract

We study the magnetism of the hole doped CuO2 spin chains in Sr14Cu24O41 by measuring the Electron Spin Resonance (ESR) and the static magnetization M in applied magnetic fields up to 14 T. In this compound, the dimerized ground state and the charge order in the chains are well established. Our experimental data suggest that at low temperatures the Curie-like increase of M as well as the occurrence of the related ESR signal are due to a small amount of paramagnetic centers which are not extrinsic defects but rather unpaired Cu spins in the chain. These observations qualitatively confirm recent ab initio calculations of the ground state properties of the CuO2 chains in Sr14Cu24O41. Our complementary quantum statistical simulations yield that the temperature and field dependence of the magnetization can be well described by an effective Heisenberg model in which the ground state configuration is composed of spin dimers, trimers, and monomers.