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 °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) 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 “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 TN (ranging from 3 to 17 K), with additional transitions observed at lower temperatures for the Tb and Dy members.

The average structure of RECrxGe2 corresponds to the CeNiSi2-type, with Cr atoms entering square pyramidal sites. The Cr atoms provide no contribution to the effective magnetic moment in these compounds, which undergo antiferromagnetic ordering below 20 K.Figure optionsDownload as PowerPoint slide