In order to explore the physical properties of orthorhombic U2Co3Si5-type Sm2Ru3Ge5, 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 Cp. An antiferromagnetic phase transition at the Néel temperature TN≃7K has been identified by all measured physical quantities. Remarkably, another intrinsic phase transition characterized by marked features has been discerned at T∗≃240K. The distinct peak in Cp 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 Sm2Ru3Ge5 with the tetragonal Sc2Fe3Si5-type structure which was recently reported to exhibit the coexistence of magnetic and CDW phase transitions. On this basis, the observed features in orthorhombic Sm2Ru3Ge5 have been discussed by comparing with the results in tetragonal Sm2Ru3Ge5 as well as other CDW systems.
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