Spin fluctuation effects in substituted CeRu<SUB>2</SUB>Si<SUB>2</SUB> and YbPd<SUB>2</SUB>Si<SUB>2</SUB> alloys

Effects of chemical substitution in CeRu2Si2, a well-studied heavy fermion system and YbPd2Si2 have been investigated through magnetic susceptibility and X-ray diffraction in the systems CeRuxSi2, CeRu2&#8722;xOsxSi2, CeRu2Si2&#8722;x Gex and YbPd2Si2&#8722;x Gex. Replacing silicon by germanium generates normal chemical pressure effect, namely, Ce and Yb atoms in CeRu2Si2 and YbPd2Si2 became more and less magnetic respectively. With increasing Ge concentration, CeRu2Si2&#8722;x Gex exhibits larger susceptibility at low temperature, goes to an antiferromagnetic state and finally becomes ferromagnetic. In YbPd2Si2&#8722;xGex , increasing Ge concentration drives Yb atoms to more divalent state. Electronic effects are more pronounced in CeRu2&#8722;xOsx Si2 though CeRu2Si2 and CeOs2Si2 have very nearly the same lattice parameters. It is conjectured that CeRu2Si2&#8722;xGex may be the first Ce-based heavy fermion having a magnetic ground state