Crystal structures and magnetic properties of NdCoAl4, Nd2Co3Al9 and SM2Co3Al9

The new compounds, NdCoAl4, Nd2Co3Al9 and Sm2Co3Al9 have been prepared by arc-melting of the elemental components. The chemical and structural characterizations were carried out on both as-cast and annealed samples using X-ray diffractometry, metallographic analysis and EDS-microanalysis. The crystal structures of NdCoAl4 and Nd2Co3Al9 were refined from the single-crystal X-ray diffraction data, collected at room temperature. NdCoAl4 adopts the LaCoAl4 type of structure, crystallizing with the orthorhombic space group Pmma (no. 51), in a unit cell of dimensions: a=7.6574(3) angstrom, b=4.0401(1) angstrom, c=6.8499(3) angstrom. Nd2CO3Al9 crystallizes in the orthorhombic space group Cmcm (n degrees 63), with the lattice parameters: a=12.8911(4) angstrom, b=7.5594(2) angstrom, c=9.4703(2) angstrom. Nd2CO3Al9 and Sm2Co3Al9 are isostructural to the (Y2CoGa9)-Ga-3-type. Magnetic susceptibility measurements, recorded in the temperature range 1.7-300 K, have revealed that all phases orders antiferromagnetically at low temperature. The Neel temperature are 2.8, 3.0 and 6 K for NdCoAl4, Nd2Co3Al9 and Sm2Co3Al9, respectively. At high temperature, the paramagnetic domain is dominated by the contribution of the rare-earth ions. (c) 2005 Elsevier B.V. All rights reserved.