The magnetic nature of the altermagnet candidate ${\mathrm{RuO}}_2$ remains under debate. It has been recently shown from quantum oscillations and angle-resolved photoemission spectroscopy that the high-quality ${\mathrm{RuO}}_2$ bulk single crystal is a paramagnetic metal. Here we report the specific heat and magnetic susceptibility in ultraclean ${\mathrm{RuO}}_2$ single crystals with residual resistivity ratio up to 1200. The electronic specific heat, the magnetic susceptibility, and the $T^2$ coefficient in resistivity point to a weakly correlated three-dimensional Fermi-liquid state, as supported by the Wilson and Kadowaki-Woods ratios. The magnetic susceptibility increases with temperature and is phenomenologically fitted with an inclusion of $T\text{ln}(T/T_0)$ over a wide temperature range up to 400 K. In contrast, the energy dependence of the density of states and thermal activation of quasiparticles lead to a decrease with temperature. Such characteristic temperature dependence, similar to that observed in other $d$-electron metals, is attributable to an enhanced orbital contribution arising from lattice-expansion-induced changes in the band structure.

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• Magnetic susceptibility
• Magnetism
• Specific heat
• Altermagnets
• Paramagnets
• Quantum dots
• Single crystal materials
• DC susceptibility measurements
• Resistivity measurements
• Specific heat measurements