competition of kondo spin fluctuations and RKKY interactions in CeRh<SUB>2</SUB>si<SUB>2-x</SUB>Ge<SUB>x</SUB> and CeM<SUB>2</SUB>X<SUB>2</SUB> compounds: a kondo necklace problem

We present the results of our measurements of the lattice constants and magnetic susceptibility of the pseudo-ternary system CeRh2Si2-xGex which crystallizes in the tetragonal ThCr2Si2 structure. Both of the cell constants a and c increase linearly with x. The magnetic ordering temperature TN exhibits initially an enhancement with the increase in x (TN=36.9 K for x=0 and 38.3 K for x=0.125) and then decreases as x continues to increase further. These results, along with those on the pressure dependence of TN in CeRh2Si2, can be understood on the basis of the Doniach's model of a Kondo necklace. We discuss also the applicability of this model to describe the strong correlation between the structural aspects and the ground-state properties of the whole series of Ce-based ternaries CeM2X2(M=3d, 4d and 5d elements; X = Si, Ge) of the ThCr2Si2 structure