Magnetic, calorimetric, and transport properties ofCe(Pd1−xNix)2Ge2andCeNi2(Ge1−ySiy)2

Abstract

We present results of a systematic study of the isoelectronic Kondo-lattice compounds ${\mathrm{C}\mathrm{e}(\mathrm{P}\mathrm{d}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}{)}_{2}{\mathrm{Ge}}_{2}$ and ${\mathrm{CeNi}}_{2}{(\mathrm{G}\mathrm{e}}_{1\ensuremath{-}y}{\mathrm{Si}}_{y}{)}_{2}.$ With increasing x and y the hybridization of the localized $4f$ moments with the band states increases. Consequently the magnetic order of the Pd-rich compounds becomes suppressed, yielding a heavy-fermion behavior in ${\mathrm{CeNi}}_{2}{\mathrm{Ge}}_{2}$, and an intermediate valence state in Si-rich alloys. The electrical resistivity, magnetic susceptibility, and specific heat were investigated for temperatures 0.1$lTl$300 K. The antiferromagnetic order of localized spins in ${\mathrm{C}\mathrm{e}(\mathrm{P}\mathrm{d}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}{)}_{2}{\mathrm{Ge}}_{2}$ diminishes for $xg~0.9$ and intermediate valent behavior evolves for $y\ensuremath{\gtrsim}0.3$. We find significant deviations from Fermi-liquid behavior in a broad concentration range, which extends from $x=0.9$ into the intermediate valence regime $(y=0.4)$. The results are compared with model predictions for magnetic systems close to a quantum critical point and for systems with frozen-in magnetic disorder (Griffiths phase). And although we find qualitatively the fingerprints of a quantum critical point, resistivity and heat capacity cannot be explained coherently within the same model.