CeCu2Si2: More nearly magnetic thanUBe13

We have prepared and studied, via dc and ac susceptibility and specific heat, samples of ${\mathrm{Ce}}_{1\mathrm{-}\mathit{x}}$ ${\mathit{M}}_{\mathit{x}}$ ${\mathrm{Cu}}_{2.2}$ ${\mathrm{Si}}_2$, with M=Y, La, and Lu. All samples show an increase in the Wilson ratio, ∝χ/γ, with the low-temperature χ per Ce mole increasing from Lu to Y to La and ${\mathrm{Ce}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{La}}_{\mathit{x}}$ ${\mathrm{Cu}}_{2.2}$ ${\mathrm{Si}}_2$ actually having χ(1.8 K) per Ce mole larger than in pure ${\mathrm{CeCu}}_{2.2}$ ${\mathrm{Si}}_2$ for x>0.5. The low-temperature specific heat of ${\mathrm{CeCu}}_{2.2}$ ${\mathrm{Si}}_2$ is enhanced by dilution by La, when normalized per Ce mole, whereas dilution by Y and Lu strongly depresses the per-Ce-mole specific heat. These two contrasting effects may be linked to a volume effect, since Y and Lu contract the ${\mathrm{CeCu}}_{2.2}$ ${\mathrm{Si}}_2$ lattice while La expands it. The fact that dilute Ce in the expanded host lattice ${\mathrm{Ce}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{La}}_{\mathit{x}}$ ${\mathrm{Cu}}_{2.2}$ ${\mathrm{Si}}_2$ has increased χ and γ at low temperatures argues for a nearness to magnetism (substantiated by recent work on ${\mathrm{Ce}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Th}}_{\mathit{x}}$ ${\mathrm{Cu}}_{2.2}$ ${\mathrm{Si}}_2$) that contrasts with results for ${\mathrm{U}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{M}}_{\mathit{x}}$ ${\mathrm{Be}}_{13}$.