Structure and magnetic properties of rare-earth chromium germanides RECrxGe2 (RE = Sm, Gd-Er)

The ternary rare-earth chromium germanides RECrxGe2 (RE = Sm, Gd-Er) have been obtained by reactions of the elements, either in the presence of tin or indium flux, or through arc-melting followed by annealing at 800 degrees C. The homogeneity range is limited to 0.25 <= x <= 0.50 for DyCrxGe2. Single-crystal and powder X-ray diffraction studies on the RECr0.3Ge2 members revealed that they adopt the CeNiSi2-type structure (space group Cmcm, Z = 4, a = 4.1939(5)-4.016(2) angstrom, b = 16.291(2)-15.6579(6) angstrom, c = 4.0598(5)-3.9876(2) angstrom in the progression for RE = Sm to Er), which can be considered to be built up by stuffing transition-metal atoms into the square pyramidal sites of a "REGe2" host with the ZrSi2-type structure. (The existence of YbCr0.3Ge2 is also implicated.) Only the average structure was determined here, because Unusually short Cr-Ge distances imply the development of a superstructure involving distortions of the square Ge net. Magnetic measurements on RECr0.3Ge2 (RE = Gd-Er) indicated that antiferromagnetic ordering sets in below T-N (ranging from 3 to 17K), with additional transitions observed at lower temperatures for the Tb and Dy members. (C) 2008 Elsevier Inc. All rights reserved.