Crystal Structure and Magnetic Properties of the Lanthanoid Platinum GermanidesLnPtGe (Ln=Ce, Pr, Nd, Sm)

Abstract

The crystal structures of the title compounds were reinvestigated. The previously reported KHg2(CeCu2) type structure with statistical distribution of the platinum and germanium atoms corresponds only to the subcell of the ordered orthorhombic YPdSi type structure (Pmmn, Z=8) of these compounds, which was refined from single-crystal X-ray diffractometer data of CePtGe:a=445.0(1) pm,b=1464.8(3) pm,c=761.8(2) pm; PrPtGe:a=444.01(3) pm,b=1456.57(9) pm,c=761.71(5) pm; and the low-temper- ature (α) modification of SmPtGe:a=440.0(1) pm,b=1428.1(2) pm,c=756.6(1) pm. Nevertheless, some evidence for disorder was obtained from the refinement of the occupancy parameters of these compounds. The results suggest the substitution of germanium by platinum atoms and/or vice versa in the order of a few at%. The high-temperature (β) modification of SmPtGe with TiNiSi type structure was confirmed by a refinement from single crystal diffractometer data. The magnetic properties of these compounds were investigated with a SQUID magnetometer. CePtGe, PrPtGe, and NdPtGe follow the Curie–Weiss law with magnetic moments close to those of the trivalent rare earth elements. The magnetic properties ofα- andβ-SmPtGe are dominated by the Van Vleck paramagnetism of the samarium atoms. Antiferromagnetic ordering was detected for CePtGe, NdPtGe, and both modifications of SmPtGe with Néel temperatures between 4 and 6 K, while PrPtGe remains paramagnetic down to 2 K. The crystal structures of these compounds are briefly discussed together with those of the LaPtSi and LaIrSi type structures, which occur for LaPtGe and EuPtGe, respectively.