We present a comprehensive study of single crystals of ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$, a putative Kitaev honeycomb magnet, focusing on its low-temperature phase behaviors. A new thermal phase transition is identified at 31.0 K, below which the system develops a two-dimensional (2D) long-range magnetic order. This order precedes the well-known three-dimensional (3D) order below 26.7 K, and is likely driven by strongly anisotropic interactions. Surprisingly, excitations from the 3D order do not support the order's commonly accepted “zigzag” nature, and are instead consistent with a “triple-$\mathbf{q}$” description, which has remained hitherto unexplored in the study of Kitaev honeycomb magnets. The 3D order exerts a fundamental feedback on high-energy excitations that likely involve orbital degrees of freedom, and it features strongly scattered spin waves until at much lower temperatures, a sign for ground state near degeneracy and frustration. These findings constrain microscopic models and render ${\mathrm{Na}}_2{\mathrm{Co}}_2{\mathrm{TeO}}_6$ a spin-orbit entangled frustrated magnet that hosts very rich physics.

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• Antiferromagnetism
• Quantum spin liquid
• Spin state transition
• Antiferromagnets
• Honeycomb lattice
• Single crystal materials
• Inelastic light scattering
• Inelastic neutron scattering
• Neutron diffraction
• Nuclear spin resonance
• Resonant elastic x-ray scattering
• Specific heat measurements
• Time-of-flight neutron spectroscopy