MAGNETIC-ORDERING IN (U0.5TB0.5)CO2GE2, STUDIED BY AC-SUSCEPTIBILITY AND NEUTRON-DIFFRACTION MEASUREMENTS

UCo2Ge2, TbCo2Ge2 and their intermediate solid solution, (U0.5Tb0.5)Co 2Ge2, crystallize in the ThCr2Si2-type structure. AC-susceptibility of the latter at 20-295 K yields paramagnetic values mu(eff) = 7.3+/-0.5 mu(B) and theta = -50+/-15 K, and two magnetic transitions at 80 and 50 K. The magnetic structure observed by powder neutron diffraction at approximate to 10 K is AF-I (+ - + -) [with wavevector k=(0, 0, 1)], characterized by (U, Tb) planes stacked antiferromagnetically with ord ered moments along the tetragonal axis. The calculated average ordered magnetic moment per (U, Tb) atom, 4.05+/-0.03 mu(B), is compared with those of Tb in TbCo2Ge2 and U in UCo2Ge2, leading to a proposal of fe rromagnetic (U, Tb) planes with anti ferromagnetic coupling of U and T b moments.