Two-magnon Raman scattering from the Cu3O4 layers in (Sr,Ba)2Cu3O4Cl2

TL;DR

This study uses Raman spectroscopy to analyze two-magnon scattering in (Sr,Ba)2Cu3O4Cl2, revealing magnetic interactions and sublattice dynamics in these antiferromagnetic insulators related to cuprate parent compounds.

Contribution

First detailed Raman analysis of magnetic excitations in (Sr,Ba)2Cu3O4Cl2, identifying two-magnon features and estimating exchange coupling constants for two magnetic sublattices.

Findings

Identified two distinct two-magnon scattering features at ~3000 and ~300 cm$^{-1}$.

Estimated exchange coupling constants J$_{I}$ and J$_{II}$ for Cu$_{I}$ and Cu$_{II}$ sublattices.

Observed magnetic-related modes at ~480 and 445 cm$^{-1}$ that disappear at the Cu$_{II}$ ordering temperature.

Abstract

(Sr$_{2}$,Ba$_{2}$)Cu$_{3}$O$_{4}$Cl$_{2}$ are antiferromagnetic insulators which are akin to the parent compounds of the cuprate superconductors but with two distinct magnetic ordering temperatures related to two magnetic Cu$_{I}$ and Cu$_{II}$ spin sublattices. Here we present a study of these materials by means of Raman spectroscopy. Following the temperature and polarization dependence of the data we readily identify two distinct features at around 3000 cm$^{-1}$ and 300 cm$^{-1}$ that are related to two-magnon scattering from the two sublattices. The estimated spin-exchange coupling constants for the Cu$_{I}$ and Cu$_{II}$ sublattices are found to be J$_{I}\sim$139-143(132-136) meV and J$_{II}\sim$14(11) meV for Sr(Ba) compounds. Moreover, we observe modes at around 480 and 445 cm$^{-1}$ for the Sr and Ba containing samples respectively, that disappears at the ordering temperature of the Cu$_{II}$. We argue that this modes may also be of magnetic origin and possibly related to interband transitions between the Cu$_{I}$-Cu$_{II}$ sublattices.