High-temperature magnetic anomaly via suppression of antisite disorder through synthesis route modification in a Kitaev candidate Cu$_2$IrO$_3$

TL;DR

This study demonstrates that modifying synthesis conditions reduces antisite disorder in Cu$_2$IrO$_3$, revealing a magnetic anomaly near 70 K and suggesting the spin-disordered state is extrinsic, influenced by synthesis rather than intrinsic properties.

Contribution

The paper introduces a synthesis route modification that significantly decreases antisite disorder in Cu$_2$IrO$_3$, clarifying the intrinsic magnetic behavior of the material.

Findings

Reduced synthesis temperature from 350°C to 170°C.

Decreased antisite disorder from 19% to 5%.

Observed magnetic anomaly at ~70 K.

Abstract

By incorporating inert KCl into the Na$_2$IrO$_3$ + 2CuCl $\to$ Cu$_2$IrO$_3$ + 2NaCl topochemical reaction, we significantly reduced the synthesis temperature of Cu$_2$IrO$_3$ from the 350$^\circ$C reported in previous studies to 170$^\circ$C. This adjustment decreased the Cu/Ir antisite disorder concentration in Cu$_2$IrO$_3$ from $\sim$19$\%$ to $\sim$5$\%$. Furthermore, magnetic susceptibility measurements of the present Cu$_2$IrO$_3$ sample revealed a weak ferromagnetic-like anomaly with hysteresis at a magnetic transition temperature of $\sim$70 K. Our research indicates that the spin-disordered ground state reported in chemically disordered Cu$_2$IrO$_3$ is an extrinsic phenomenon, rather than an intrinsic one, underscoring the pivotal role of synthetic chemistry in understanding the application of Kitaev model to realistic materials.