Magnetism and superconductivity inM5Rh4Ge10(M=Gd, Tb, Dy, Ho, Er, Tm, Lu, and Y)

Abstract

Low-temperature resistivity, magnetization and heat-capacity studies are reported for the isostructural $M_5{\mathrm{Rh}}_4{\mathrm{Ge}}_{10}\hspace{0.5em}(M=\mathrm{G}\mathrm{d},\mathrm{}\mathrm{T}\mathrm{b},\mathrm{}\mathrm{D}\mathrm{y},\mathrm{}\mathrm{H}\mathrm{o},\mathrm{}\mathrm{E}\mathrm{r},\mathrm{}\mathrm{T}\mathrm{m},\mathrm{}\mathrm{L}\mathrm{u},$ and Y) series. Some of the compounds $(M=\mathrm{G}\mathrm{d},\mathrm{}\mathrm{T}\mathrm{b},\mathrm{}\mathrm{E}\mathrm{r},$ and Tm) show multiple magnetic transitions below 15 K while others (M=Dy and Ho) exhibit only a single magnetic transition. The four magnetic transitions observed for ${\mathrm{Gd}}_5{\mathrm{Rh}}_4{\mathrm{Ge}}_{10}$ and ${\mathrm{Tb}}_5{\mathrm{Rh}}_4{\mathrm{Ge}}_{10}$ are unusual in that the one at the highest temperature is a second-order phase transition while the other three are first-order transitions probably involving moment reorientations. An anisotropic exchange interaction is proposed as the cause of the multiple transitions. Of the nonmagnetic compounds, ${\mathrm{Lu}}_5{\mathrm{Rh}}_4{\mathrm{Ge}}_{10}$ shows superconductivity below 2.4 K whereas ${\mathrm{Y}}_5{\mathrm{Rh}}_4{\mathrm{Ge}}_{10}$ remains normal down to 1.7 K. The results are compared with those of the previously investigated $M_5{\mathrm{Ir}}_4{\mathrm{Si}}_{10}$ series.