Calorimetric and transport investigations of ${\mathrm{CePd}}_{2+x}{\mathrm{Ge}}_{2-x}$ $(x=0\mathrm{}$ and $0.02)$ up to 22 GPa

The influence of pressure on the magnetically ordered ${\mathrm{CePd}}_{2.02}{\mathrm{Ge}}_{1.98}$ has been investigated by a combined measurement of electrical resistivity $\rho \mathrm{}\left(T\right)\mathrm{}$ and ac calorimetry $C\left(T\right),$ for temperatures in the range $0.3\hspace{0.5em}\mathrm{K}<T<\mathrm{}10\mathrm{}\hspace{0.5em}\mathrm{K}$ and pressures p up to 22 GPa. Simultaneously, ${\mathrm{CePd}}_2{\mathrm{Ge}}_2$ has been examined by $\rho \mathrm{}\left(T\right)\mathrm{}$ down to 40 mK. In ${\mathrm{CePd}}_{2.02}{\mathrm{Ge}}_{1.98}$ and ${\mathrm{CePd}}_2{\mathrm{Ge}}_2$ the magnetic order is suppressed at a critical pressure $p_c=11.0\mathrm{}\hspace{0.5em}\mathrm{GPa}$ and $p_c=13.8\mathrm{}\hspace{0.5em}\mathrm{GPa},$ respectively. In the case of ${\mathrm{CePd}}_{2.02}{\mathrm{Ge}}_{1.98}$ the temperature coefficient A of $\rho \mathrm{}\left(T\right)\mathrm{}$ not only indicates the loss of magnetic order but also the ac signal ${1/V}_{\mathrm{ac}}\propto C/T$ recorded at low temperature. The residual resistivity is extremely pressure sensitive and passes through a maximum and then a minimum in the vicinity of $p_c.$ The $\mathrm{}(T,p)\mathrm{}$ phase diagram and the $A\left(p\right)\mathrm{}$ dependence of both compounds can be qualitatively understood in terms of a pressure-tuned competition between magnetic order and the Kondo effect according to the Doniach picture. The temperature-volume $\mathrm{}(T,V)\mathrm{}$ phase diagram of ${\mathrm{CePd}}_2{\mathrm{Ge}}_2$ combined with that of ${\mathrm{CePd}}_2{\mathrm{Si}}_2$ shows that in stoichiometric compounds mainly the change of interatomic distances influences the exchange interaction. It will be argued that in contrast to this the much lower $p_c$ value of ${\mathrm{CePd}}_{2.02}{\mathrm{Ge}}_{1.98}$ is caused by an enhanced hybridization between $4f$ and conduction electrons.