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.