Magnetic ordering in U(M,M′)2Ge2 compounds (M,M′=Co,Ni,Cu)

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Abstract
Several U(M,M’)2Ge2 compounds (M,M’=Co,Ni,Cu) have been studied by neutron diffraction. U(Co1−xCux)2Ge2 and UNiCuGe2 exhibit ThCr2Si2‐type tetragonal structure, with a=4.02–4.10 Å and c=9.86–10.25 Å, and a magnetically ordered uranium sublattice with moments along c. The ordering is antiferromagnetic with a wave vector k=(0,0,1) for x=0,0.25, and 0.50 and UNiCuGe2 (TN=175, 130, 100, and 140 K, respectively), and ferromagnetic for x=0.75 (TC=102 K) and 1 (TC=107 K). In UCoNiGe2 (a=4.07 Å, c=9.52 Å) no magnetic ordering has been found down to 10 K. Two other samples of UCo2Ge2 (a=4.04 Å, c=9.44 and 9.38 Å) were previously reported not to order magnetically down to 4.2 K. The absence of magnetic ordering is related to smaller c parameters and lower crystal symmetry.