We present magnetization and dilatometry measurements on the honeycomb cobaltate ${\mathrm{Na}}_3{\mathrm{Co}}_2{\mathrm{SbO}}_6$ and map out its detailed field-temperature phase diagram down to sub-Kelvin temperatures. Our data for in-plane magnetic fields show a strongly anisotropic $c^{*}$-axis lattice response, which is dominated by the variation of Co–O–Co bond angles according to ab initio calculations. At $T=0.4\mathrm{K}$, the magnetization $M\left(B\right)$ exhibits steplike features that are also highly anisotropic. In the case of $B\parallel b$, a small hysteresis observed around the second field-induced magnetic transition ($B_{c2}$) indicates its first-order character, whereas the apparent divergence of the magnetic Grüneisen parameter at $B_{c2}$ is suppressed upon cooling and signals the absence of quantum critical behavior upon entering the field-polarized state. None of our thermodynamic measurements provide evidence for a field-induced quantum spin-liquid state near or above $B_{c2}$.

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• Frustrated magnetism
• Magnetic phase transitions
• Magnetism
• Spin liquid
• Thermal expansion
• Crystal growth
• DFT+U
• Kitaev model