UCoNiGe 2, nonmagnetic solid solution of the antiferromagnets UCo 2Ge 2 and UNi 2Ge 2

Abstract

The compounds UCo 2Ge 2 and UNi 2Ge 2 crystallize in the body-centered tetragonal ThCr 2Si 2-type structure (space group 14/mmm) and order with the AF-1 antiferromagnetic structure [ k = (0, 0, 1)] . Two polycrystalline samples of UCoNiGe 2, an intermediate solid solution of these compounds, have been prepared under identical conditions and studied by x-ray and neutron diffraction. Both samples crystallize in the lower-symmetry primitive tetragonal CaBe 2Ge 2-type structure (space group P4/nmm). The cobalt/nickel distribution in the M= ( Co, Ni) planes in both samples is not random, with Co:Ni ratios of 36:64 in M2 planes, close to U planes, and 64:36 in doubly dense and distant M1 planes. Absence of magnetic order in UCoNiGe 2 down to 10 K, is associated with its lower symmetry.