SINGLE-CRYSTAL NEUTRON-DIFFRACTION STUDIES ON CECU2GE2 AND CECU1.9NI0.1GE2

We have performed single-crystal neutron diffraction studies on CeCu2G e2 and CeCu1.9Ni0.1Ge2 to get insight into the very unusual magnetic p roperties of these compounds. CeCu2Ge2 orders antiferromagnetically be low T-N=4.15 K in an incommensurate sinusoidal amplitude modulated str ucture. CeCu1.9Ni0.1Ge2 shows two successive magnetic phase transition s at T-N1=3.65 K and T-N2=2.65 K, respectively. The corresponding magn etic structures are very similar to each other as well as to the magne tic structure of pure CeCu2Ge2. Based on the temperature dependence of the intensities of the principal magnetic reflections, the two magnet ic phases seem to superimpose independently of each other.