Magnetic behaviour of RRhAl (R=La, Ce, Pr, Nd and Gd) compounds

Magnetization and electrical resistivity measurements have been carried out on ternary intermetallic compounds of the formula RRhAl (R=La, Ce, Pr, Nd and Gd). These compounds with R=La and Ce crystallize in the orthorhombic Pd2(MnPd)Ge2 type structure while those with R=Pr, Nd and Gd crystallize in the orthorhombic TiNiSi type structure, all in the space group Pnma. The compound LaRhAl exhibits superconductivity below 2.4 K while PrRhAl, NdRhAl and GdRhAl are ferromagnetically ordered with Curie temperatures of about 5, 10 and 30 K, respectively. The compound CeRhAl shows mixed valent behaviour of the Ce ions and is neither magnetically ordered nor superconducting down to 1.7 K.