ORDERED MAGNETIC-MOMENTS IN (A,A)CO2GE2 SYSTEMS

The relative orientation of ordered magnetic moments of f-atoms (A,A') occupying randomly the same site, has been studied by powder neutron diffraction in the magnetically-ordered state of (A,A')Co2Ge2 solid so lutions. These materials crystallize in the ThCr2Si2-type structure an d order antiferromagnetically in the AF-I structure, characterized by ferromagnetic (A,A') basal planes stacked alternately (+-+-) along the tetragonal axis, with A and A' moments aligned along this axis. The ' spin-charge' concept, which accounts for antiparallel orientation of l ight and heavy lanthanide moments in (Nd1-xTbx)Co2Ge2, is found to app ly also to uranium and terbium moments in (U1-xTbx)Co2Ge2. The paralle l orientation of uranium and neodymium moments, observed in (U1-xNdx)C o2Ge2, also follows the 'spin-charge' concept. Uranium and terbium mom ent compensation (in basal planes of zero total moment) is anticipated for a (U1-xTbx)Co2Ge2 solid solution with x approximate to 0.15. (C) 1998 Elsevier Science S.A.