High-temperature magnetic anomaly via suppression of antisite disorder through synthesis route modification in a Kitaev candidate Cu 2 IrO 3 .

By incorporating inert KCl into the Na 2 IrO 3 + 2CuCl → Cu 2 IrO 3 + 2NaCl topochemical reaction, we significantly reduced the synthesis temperature of Cu 2 IrO 3 from the 350 °C reported in previous studies to 170 °C. This adjustment decreased the Cu/Ir antisite disorder concentration in Cu 2 IrO 3 from ∼19% to ∼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 ∼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.