Hyperhoneycomb Iridate β-li2iro3 As A Platform For Kitaev Magnetism

A complex iridium oxide β-Li2IrO3 crystallizes in a hyperhoneycomb structure, a three-dimensional analogue of honeycomb lattice, and is found to be a spin-orbital Mott insulator with Jeff=1/2 moment. Ir ions are connected to the three neighboring Ir ions via Ir-O2-Ir bonding planes, which very likely gives rise to bond-dependent ferromagnetic interactions between the Jeff=1/2 moments, an essential ingredient of Kitaev model with a spin liquid ground state. Dominant ferromagnetic interaction between Jeff=1/2 moments is indeed confirmed by the temperature dependence of magnetic susceptibility χ(T) which shows a positive Curie-Weiss temperature θCW∼+40K. A magnetic ordering with a very small entropy change, likely associated with a noncollinear arrangement of Jeff=1/2 moments, is observed at Tc=38K. With the application of magnetic field to the ordered state, a large moment of more than 0.35μB/Ir is induced above 3 T, a substantially polarized Jeff=1/2 state. 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