Role of Disorder in Governing the Magnetic Properties of Cu2IrO3

TL;DR

This study investigates how disorder influences the magnetic properties of Cu$_2$IrO$_3$, revealing that synthesis-dependent disorder leads to complex magnetic states including fluctuating clusters and spin freezing.

Contribution

It provides a detailed structural and electronic characterization linking disorder to magnetic ground states in Cu$_2$IrO$_3$, highlighting the importance of synthesis conditions.

Findings

Large antisite disorder (~25%) detected.

Mixed valence states of Cu and Ir identified.

Disorder induces magnetic frustration and cluster freezing.

Abstract

Cu$_2$IrO$_3$ is a honeycomb iridate which has been studied recently as a candidate Kitaev quantum spin liquid. Its magnetic ground state however, has been reported to be quantum disordered, spin glassy, or magnetically ordered depending on synthesis details. We have prepared a Cu$_2$IrO$_3$ sample with large antisite disorder and studied in detail its structure (global and local), charge states, and thermodynamic properties to try to quantify and characterize the disorder and its connection to the magnetic ground state. X-ray diffraction, Extended x-ray absorption fine structure(EXAFS) and X-ray pair distribution function analysis revealed a large site disorder ($\sim$25\%), while XPS and XANES reveal mixed valence of Cu and Ir following Cu$^{1+}$ + Ir$^{4+}$ $\rightarrow$ Cu$^{2+}$ + Ir$^{3+}$. This combination of site disorder and charge redistribution generates competing antiferromagnetic interactions and magnetic frustration, resulting in dynamically fluctuating AFM clusters near 80K that freeze below 29K. These results demonstrate the crucial role of synthesis dependent disorder in determining the magnetic ground state of Cu$_2$IrO$_3$.