Crystal structure and magnetic properties of the lanthanoid platinum germanides LnPtGe (Ln = Ce, Pr, Nd, Sm)

The crystal structures of the title compounds were reinvestigated. The prev iously reported KHg2 (CeCu2) type structure with statistical distribution o f the platinum and germanium atoms corresponds only to the subcell of the o rdered orthorhombic YPdSi type structure (Pmmn, Z=8) of these compounds, wh ich 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-temperature (alpha) modific ation of SmPtGe: a = 440.0(1) pm, b = 1428.1(2) pm, c = 756.6(1) pm. Nevert heless, some evidence for disorder was obtained from the refinement of the occupancy parameters of these compounds. The results suggest the substituti on of germanium by platinum atoms and/or vice versa in the order of a few a t%. The high-temperature (beta) modification of SmPtGe with TiNiSi type str ucture was confirmed by a refinement from single crystal diffractometer dat a. The magnetic properties of these compounds were investigated with a SQUI D magnetometer. CePtGe, PrPtGe, and NdPtGe follow the Curie-Weiss law with magnetic moments close to those of the trivalent rare earth elements. The m agnetic properties of alpha- and beta-SmPtGe are dominated by the Van Vleck paramagnetism of the samarium atoms. Antiferromagnetic ordering was detect ed for CePtGe, NdPtGe, and both modifications of SmPtGe with Neel temperatu res between 4 and 6 K, while PrPtGe remains paramagnetic down to 2 K, The c rystal structures of these compounds are briefly discussed together with th ose of the LaPtSi and LaIrSi type structures, which occur for LaPtGe and Eu PtGe, respectively. (C) 1999 Academic Press.