Thermodynamics and heat transport of a disordered antiferromagnet 3R-Na₂MnTeO₆

We study the low-temperature thermal conductivity, specific heat and magnetic susceptibility of 3R-Na₂MnTeO₆ single crystal, which is a layered antiferromagnet. Magnetic susceptibility shows no magnetic transition at low temperatures down to 2 K, while the antiferromagnetic interaction was confirmed by the negative Curie-Weiss temperatures for both interlayer and intralayer susceptibility. Ultralow-temperature specific heat down to 80 mK also displays the absence of magnetic ordering. Whereas, the low-temperature ac susceptibility indicates spin freezing around 1 K. Ultralow-temperature thermal conductivity shows a T²-dependence with very small magnitude, which seems to be compatible with the spin glass state. However, both the in-plane and out-of-plane magnetic fields suppress the thermal conductivity rather strongly, which is quite different from the known behavior of that in the spin glass systems. These results suggest a ground state with spin freezing rather than the canonical spin glass.