The (U1-xLnx)Co2Ge2 systems: parallel (Ln = Nd) and antiparallel (Ln Tb) magnetic f-moments in the ordered state, determined by neutron diffraction

The relative orientation of magnetic moments of uranium (5f-atom) and a lanthanide (Ln, 4f-atom), occupying randomly the same site, was investigated by neutron diffraction in the ordered state of the systems (U1-xLnx)Co2Ge2 with light (Ln = Nd) and heavy (Ln = Tb) lanthanide. These materials crystallize in the ThCr2Si2-type structure. Most of them order in the antiferromagnetic AF-I structure, with alternate (+ -) stacking of (U, Ln) planes having net moment, and f-moments along the tetragonal axis. It is found that the U and Nd moments in (U1-xNdx)Co2Ge2 are parallel, while the U and Tb moments in (U1-xTbx)Co2Ge2 are antiparallel. This is apparently due to in-plane direct exchange between f-atoms, in agreement with the ''spin-charge'' concept, considering that the U moments behave like light Ln. (orig.)