Magnetism in the honeycomb layers of Na₂Ni₂TeO₆ with chiral layers of Na

Low dimensional magnetic lattices offer the possibility of realizing flatbands in the magnon spectrum which can then lead to dissipation-less spin transport and associated magnon Hall effect. One could expect to find a magnon insulator, similar to a topological insulator. In the present work we present a rather less-studied honeycomb material Na₂Ni₂TeO₆ where our preliminary density functional theory calculations of magnetic structure shows departures from reported structures. Our samples of Na₂Ni₂TeO₆ confirmed hexagonal P6₃/mcm space group with refined lattice parameters, a=5.2023(1)Å and c=11.1552(8)Å. The bulk magnetism for the present sample is characterized using magnetic susceptibility and specific heat, both of which confirm a phase transition at 28 K. Application of 8 T magnetic field only slightly polarizes the transition. We obtain a Curie-Weiss temperature of -9.7(2)K and effective paramagnetic moment of 2.24(4)m_B/Ni. This matches well with the spin-only moment of Ni²⁺. Elastic and inelastic neutron scattering experiments are currently underway and reveal a rather flat spin wave excitation at 5 meV. Combining neutron diffraction with the DFT results, we would arrive at an accurate estimation of the exchange constants for Na₂Ni₂TeO₆.