Evolution of magnetism in the single-crystal honeycomb iridates (Na1-xLix)2IrO3

We report the successful synthesis of single crystals of the layered iridate (Na1-xLix)(2)IrO3, 0 <= x <= 0.9, and a thorough study of its structural, magnetic, thermal, and transport properties. This compound allows a controlled interpolation between Na2IrO3 and Li2IrO3, while maintaining the quantum magnetism of the honeycomb Ir4+ planes. The measured phase diagram demonstrates a suppression of the Neel temperature T-N at an intermediate x, indicating that the magnetic orders in Na2IrO3 and Li2IrO3 are distinct. X-ray data show that for x approximate to 0.7, when T-N is suppressed the most, the honeycomb structure is least distorted, leading to the speculation that at this intermediate doping of the material is closest to the spin liquid that has been sought after in Na2IrO3 and Li2IrO3. By analyzing our magnetic data with a single-ion theoretical model we also show that the trigonal splitting on the Ir4+ ions changes sign from Na2IrO3 to Li2IrO3.