Magnetic frustration in K₂Co₂TeO₆, a honeycomb antiferromagnet

Quantum spin liquid (QSL) is an exotic state of condensed matter in which localized electron spins are strongly correlated but lack long-range magnetic order. Magnetic frustration, a key prerequisite for QSL states, can arise from strongly anisotropic, bond-dependent Kitaev interactions, which are believed to occur in α-RuCl₃​, Na₂​IrO₃, and compounds featuring honeycomb lattices of Co²⁺ ions. We performed comprehensive studies on such a new compound, K₂Co₂TeO₆​. Neutron diffraction reveals that the parent magnetic structure is a canted zigzag order with dominant AFM interlayer coupling. The system exhibits additional complexity with modulation vector (1/4, 0, 0), each surrounded by six (1/12, 0, 0) peaks of longer-range modulation. Peaks at (1/6, 1/6, 1) emerge below T_N1 as a higher-order modulation, suggesting fractal-like phenomena. The simultaneous suppression of intensity at (1/6, 0, 1) and equivalent peaks under magnetic field indicates a multiple-q magnetic structure. Persistent magnetic diffuse scattering reveals weak interlayer exchange couplings. Inelastic neutron scattering (INS) shows not only a spin excitation continuum above T_N2​ but also flat spin wave bands, which condense from the continuum and are enhanced below T_N1​. In summary, K₂Co₂TeO₆​ is a quasi-2D honeycomb antiferromagnet with a high degree of frustration, as evidenced by multiple magnetic diffraction peaks, persistent magnetic diffuse diffraction and excitation continuum, and flat spin wave bands.