Coexisting long-range zigzag antiferromagnetic order and glassy dynamics in spin-1 honeycomb lattice Na₃Ni₂SbO₆

Here, we report an interesting magnetic oxide Na₃Ni₂SbO₆, where the interplay between exchange interactions and lattice symmetry crucially influence its exotic ground state. This compound features a layered honeycomb lattice with magnetic Ni²⁺ (spin-1) surrounding nonmagnetic Sb⁵⁺ centers. The x-ray absorption and magnetic circular dichroism measurements confirm a Ni²⁺ charge state with notable spin and orbital moments at room temperature. The material exhibits antiferromagnetic (AFM) ordering around 17 K (TN) and a field-induced magnetic transition at lower temperatures. Our measurements reveal a low-temperature anomaly, likely linked to glassy behavior. The power-law magnetic specific heat suggests mixed magnon dispersion, while low magnetic entropy indicates a highly degenerate ground state. Neutron diffraction data point to a zigzag-type AFM ground state, with a reduced site moment of 1.34(3) μB/Ni²⁺ at 2.5 K that disappears near 17.2 K, consistent with bulk data. Lattice parameters show anomalies at TN and lower temperatures. Ab-initio calculations support zigzag spin order and imply a competing in-plane Ni²⁺ interactions that causes spin frustration. Overall, our combined experimental and theoretical study uncovers the microscopic magnetic ground state of Na₃Ni₂SbO₆ as a mix of long-range zigzag AFM and a glassy state, advancing the understanding of frustrated honeycomb magnets.