Physical properties of polycrystalline Sm₂PdGe₆ and Sm₂PtGe₆

The compounds Sm₂TGe₆ (T = Pd, Pt,) were synthesized and characterized by x-ray diffraction, magnetization, electrical resistivity, thermoelectric power, and specific heat measurements performed in the temperature range 2-300K. Additional resistivity and thermoelectric power measurements performed down to 0.35K have not indicated superconductivity. These compounds crystallize in the orthorhombic structure of Ce₂NiGe ₆ type and order antiferromagnetically at 23(1) and 30(1)K, respectively, showing localized magnetism of a Sm³⁺ ion with a crystal field doublet level being the ground state. Below T_N, the electrical resistivity, the thermoelectric power, and the specific heat are dominated by electron-magnon scattering with an antiferromagnetic spin-wave spectrum typical of anisotropic antiferromagnetic systems. The thermoelectric power, S, achieves medium positive values at high temperatures, indicating a hole domination in electrical transport in both samples. At low temperatures, S changes its sign and becomes negative. At about 10K a small negative maximum in S(T) occurs for both studied compounds. All the measurements carried out point to well-localized 4f-electrons in these two compounds, being strongly influenced by the crystal-electric-field effect with a significant admixture of two J-multiplets (5/2 and 7/2), typical for Sm-containing compounds.