Investigation of Ground-State Magnetic Spin Structure of the Three-Dimensional Hyperhoneycomb Na2IrO3

We propose an investigation of the ground-state magnetic spin structure of a new three-dimensional (3D) hyperhoneycomb lattice compound Na2IrO3, an analog to the two-dimensional (2D) honeycomb Kitaev spin-liquid candidates such as Li2IrO3. The Kitaev model, predicting quantum spin liquid states, has been extensively studied in 2D honeycomb materials featuring Jeff = 1/2 magnetic moments, particularly in Ir4+-based systems, but not in 3D hyperhoneycomb materials. Here, we have synthesized a new hyperhoneycomb phase of Na2IrO3. Magnetic susceptibility and specific heat measurements revealed an intrinsic antiferromagnetic-like transition at TN = 13.6 K. Notably, Na2IrO3 exhibited susceptibility behavior distinct from its structural analog Li2IrO3, suggesting a unique magnetic ground state potentially favorable for realizing a quantum spin liquid under applied magnetic fields exceeding 10 T. Due to synthesis challenges, sample sizes are limited (~300 mg), together with the large neuron absorption from Ir, it is crucial to use high-brightness neutron diffraction facilities to accurately probe the anticipated small magnetic moment (<1 μB) and potential modulated magnetic structure. Consequently, a neutron powder diffraction experiment is necessary at the WISH instrument, leveraging its exceptional brightness, capability to cover large d-spacing regions, and low background to precisely characterize the magnetic ground state.