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 Na2IrO3 + 2CuCl → Cu2IrO3 + 2NaCl topochemical reaction, we significantly reduced the synthesis temperature of Cu2IrO3 from the 350°C reported in previous studies to 170°C. This adjustment decreased the Cu/Ir antisite disorder concentration in Cu2IrO3 from ~19% to ~5%. Furthermore, magnetic susceptibility measurements of the present Cu2IrO3 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 Cu2IrO3 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.