Superconductivity and Magnetic Ordering in $RE$$_2$Pt$_3$Ge$_5$ ($RE$ = La and Pr) Single Crystals

Superconductivity and magnetic properties of rare-earth ternary germanide intermetallic compounds, $RE$$_2$Pt$_3$Ge$_5$ ($RE$ = La and Pr), are investigated. La$_2$Pt$_3$Ge$_5$ and Pr$_2$Pt$_3$Ge$_5$ single crystals were synthesized by high temperature metal flux method with Ge self flux. These two compounds were formed in U$_2$Co$_3$Si$_5$-type orthorhombic structure (space group $Ibam$) and the lattice parameters were determined using XRD of pulverized single crystals. La$_2$Pt$_3$Ge$_5$ exhibits an onset of superconducting phase transition at $T_c$ = 8.1 K, which, to the best of our knowledge, is the highest $T_c$ in U$_2$Co$_3$Si$_5$-type superconductors. Pr$_2$Pt$_3$Ge$_5$ shows both superconducting phase transition at $T_c$ = 7.9 K and antiferromagnetic transition at $T_N$ = 4.4 K. In addition, Pr$_2$Pt$_3$Ge$_5$ reveals strong magnetic anisotropy with an easy magnetic axis perpendicular to the $c$-axis, due to crystalline electric field effect. Including these results, we will discuss the nature of $RE$$_2$Pt$_3$Ge$_5$ single crystals in detail.