The evolution of the behavior of the Ce $4f$ electron with the Cu content in the alloy Ce$({\mathrm{Pd}}_{1-x}{\mathrm{Cu}}_x{)}_2{\mathrm{Si}}_2$ was investigated by determining its structural, magnetic, transport, and thermal properties. Results obtained on 15 samples with compositions distributed along the whole concentration range allow us to draw a magnetic phase diagram showing three distinct regions. The first region at low Cu concentrations corresponds to the antiferromagnetic-ordered regime. The fast suppression of this magnetic order between $x=0.2\mathrm{}$ and $x=0.25\mathrm{}$ suggests the presence of a critical point which separates this region from the second one at larger $x$ values where no magnetic order is observed. The main characteristic of this second region, which extends up to $x=0.7\mathrm{}$, is a pronounced increase of the Kondo temperature $T_K,$ from $T_K\approx 15$ K at $x=0.25\mathrm{}$ to $T_K\approx 50$ K at $x=0.7\mathrm{}$. This is in contrast with the fast decrease of $T_K$ in the region with $x>\mathrm{}0.7\mathrm{}$. In this region a small anomaly with a ferromagnetic character is observed in the specific heat arround 4 K. The change in the evolution of $T_K$ with $x$ coincides with a change in the composition dependence of the $c$ lattice parameter of the tetragonal structure, pointing to a structure-related origin of this unusual $T_K\mathrm{}\left(x\right)\mathrm{}$ behavior. This nonmonotonous $T_K\mathrm{}\left(x\right)\mathrm{}$ dependence is reproduced using local-density-approximation band-structure calculations, which show a maximum of the hybridization strength between conduction electrons and Ce $4f$ states for intermediate Cu concentrations. Such a $T_K\mathrm{}\left(x\right)\mathrm{}$ dependence which contradicts the monotonous dependence observed in all other Ce-based alloy systems is the hallmark of the Ce$({\mathrm{Pd}}_{1-x}{\mathrm{Cu}}_x{)}_2{\mathrm{Si}}_2$ alloy, which cannot be described as a Fermi-liquid system in the nonmagnetic region.

• Received 29 August 1997

DOI:https://doi.org/10.1103/PhysRevB.58.314