Structure and magnetic properties of rare-earth chromium germanides RECr xGe 2 ( RE=Sm, Gd–Er)

Abstract

The ternary rare-earth chromium germanides RECr x Ge 2 ( 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 °C. The homogeneity range is limited to 0.25⩽ x⩽0.50 for DyCr x Ge 2. Single-crystal and powder X-ray diffraction studies on the RECr 0.3Ge 2 members revealed that they adopt the CeNiSi 2-type structure (space group Cmcm, Z=4, a=4.1939(5)–4.016(2) Å, b=16.291(2)–15.6579(6) Å, c=4.0598(5)–3.9876(2) Å 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 “ REGe 2” host with the ZrSi 2-type structure. (The existence of YbCr 0.3Ge 2 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 RECr 0.3Ge 2 ( RE=Gd–Er) indicated that antiferromagnetic ordering sets in below T N (ranging from 3 to 17 K), with additional transitions observed at lower temperatures for the Tb and Dy members.