MAGNETISM OF RANDOMLY DISTRIBUTED F-ATOMS IN (U1-XNDX)CO2GE2 SOLID-SOLUTIONS

Solid solutions of the (U1-xNdx)Co2Ge2 system (x = 0.25, 0.50, 0.75) a re found by neutron diffraction to have tetragonal ThCr2Si2-type cryst al structure (space group I4/mmm), same as their end compounds (x = 0, 1). In the solid solutions, U and Nd atoms are randomly distributed i n the basal planes. The end compounds and the solid solutions are para magnetic at room temperature; At 12 K the (U,Nd) sublattice has the an tiferromagnetic AF-I magnetic structure [+ - + - stacking of ferromagn etic (U,Nd) planes along c], with moments parallel to the c axis. It i s found that within a ferromagnetic basal plane the U magnetic moments are parallel to the Nd magnetic moments, unlike (U,Tb), where they ar e antiparallel. This shows that the ''spin charge'' rule for lanthanid es extends to U-lanthanide systems. Neutron-diffraction and ac-suscept ibility results are compared in order to investigate the character of the magnetic transition in the solid solutions.