Magnetism and spin fluctuation effects in heavy-fermionCeRu2Si2induced by partial substitution of Ru and Si

The effect of chemical substitution in ${\mathrm{CeRu}}_2$ ${\mathrm{Si}}_2$, a well-studied heavy-fermion system, has been investigated through magnetic susceptibility and x-ray diffraction measurements in the systems ${\mathrm{CeRu}}_{\mathrm{x}}$ ${\mathrm{Si}}_2$, ${\mathrm{CeRu}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Os}}_{\mathrm{x}}$ ${\mathrm{Si}}_2$, ${\mathrm{CeRu}}_2$ ${\mathrm{Si}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{C}}_{\mathrm{x}}$, and ${\mathrm{CeRu}}_2$ ${\mathrm{Si}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Ge}}_{\mathrm{x}}$. Replacing silicon by carbon and germanium generates the normal chemical-pressure effect, namely Ce atoms in ${\mathrm{CeRu}}_2$ ${\mathrm{Si}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{C}}_{\mathrm{x}}$ and ${\mathrm{CeRu}}_2$ ${\mathrm{Si}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Ge}}_{\mathrm{x}}$ are, respectively, less and more magnetic than in ${\mathrm{CeRu}}_2$ ${\mathrm{Si}}_2$. With increasing Ge concentration, ${\mathrm{CeRu}}_2$ ${\mathrm{Si}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Ge}}_{\mathrm{x}}$ first exhibits a larger low-temperature susceptibility than that in pure ${\mathrm{CeRu}}_2$ ${\mathrm{Si}}_2$, then goes into an antiferromagnetic phase, and finally becomes ferromagnetic. Electronic effects are more important than the chemical-pressure effect in ${\mathrm{CeRu}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Os}}_{\mathrm{x}}$