Bond - dependent 120° exchange in honeycomb NaNi2BiO6

I will discuss recent experiments on the magnetic structure of the
honeycomb antiferromagnet NaNi₂BiO₆. We find magnetic order with moments along the c axis below T_c1 = 6.3 K and then in the honeycomb plane below T_c2 = 4.8K with a counterrotating pattern and an incommensurate ordering wave vector q = (1/3, 1/3, 0.154 ± 0.011). Neutron scattering shows half of the expected static magnetic moment remains dynamic at low temperatures, suggesting proximity to a quantum disordered phase. The ordering wave vector, in – plane magnetic correlations, and superexchange pathways are all consistent with a bond – dependent 120° compass model exchange in NaNi₂BiO₆.