In order to explore the physical properties of orthorhombic ${\mathrm{U}}_2\mathrm{C}{\mathrm{o}}_3\mathrm{S}{\mathrm{i}}_5$-type $\mathrm{S}{\mathrm{m}}_2\mathrm{R}{\mathrm{u}}_3\mathrm{G}{\mathrm{e}}_5$, we have carried out a combined study by means of the measurements of the magnetic susceptibility χ, electrical resistivity ρ, Seebeck coefficient S, and specific heat $C_p$. An antiferromagnetic phase transition at the Néel temperature $T_N\simeq 7\mathrm{K}$ has been identified by all measured physical quantities. Remarkably, another intrinsic phase transition characterized by marked features has been discerned at $T^{*}\simeq 240\mathrm{K}$. The distinct peak in $C_p$ at $T^{*}$ with the lack of thermal hysteresis behavior provides strong evidence for the second-order phase transition in nature. It is noticed that the observations near $T^{*}$ are reminiscent of a typical charge density wave (CDW) ordering. We compared the experimental results with those observed in a polymorph of $\mathrm{S}{\mathrm{m}}_2\mathrm{R}{\mathrm{u}}_3\mathrm{G}{\mathrm{e}}_5$ with the tetragonal $\mathrm{S}{\mathrm{c}}_2\mathrm{F}{\mathrm{e}}_3\mathrm{S}{\mathrm{i}}_5$-type structure which was recently reported to exhibit the coexistence of magnetic and CDW phase transitions. On this basis, the observed features in orthorhombic $\mathrm{S}{\mathrm{m}}_2\mathrm{R}{\mathrm{u}}_3\mathrm{G}{\mathrm{e}}_5$ have been discussed by comparing with the results in tetragonal $\mathrm{S}{\mathrm{m}}_2\mathrm{R}{\mathrm{u}}_3\mathrm{G}{\mathrm{e}}_5$ as well as other CDW systems.

• Received 5 November 2019
• Revised 13 February 2020
• Accepted 13 April 2020

DOI:https://doi.org/10.1103/PhysRevB.101.155140