Synthesis, structure and physical properties of GdCu4Al and GdCu4Ga

Two non-stoichiometric Gd compounds, GdCu5−xTrx (Tr=Al, Ga) have been synthesized from the corresponding elements by high temperature reactions in sealed tantalum containers. They crystallize in the hexagonal CaCu5-type (Pearsonʹs symbol hP6, space group P6/mmm, No. 191) with lattice parameters determined from single-crystal X-ray diffraction at room temperature as follows: a=5.0831(10) Å; c=4.156(2) Å for GdCu3.98(4)Al1.02(4), and a=5.1025(10) Å; c=4.155(2) Å for GdCu3.9(1)Ga1.1(1), respectively. Structure refinements from single crystal X-ray diffraction data reveal that substitution of Cu for Al or Ga takes place preferably on one of the two transition metal sites with site symmetry mmm (3g). Both compounds order antiferromagnetically below ∼40 K and ∼36 K, respectively, as determined from temperature dependent dc-magnetization, resistivity and heat-capacity measurements.