Calorimetric and transport investigations of CePd_{2+x}Ge_{2-x} (x=0 and 0.02) up to 22 GPa

TL;DR

This study investigates how pressure affects magnetic order in CePd_{2+x}Ge_{2-x} compounds up to 22 GPa, revealing suppression of magnetic order and insights into the interplay of magnetic and Kondo effects.

Contribution

It provides the first detailed pressure-dependent calorimetric and transport data for CePd_{2+x}Ge_{2-x} and links the critical pressure differences to electronic hybridization effects.

Findings

Magnetic order is suppressed at 11.0 GPa for CePd_{2.02}Ge_{1.98} and 13.8 GPa for CePd_2Ge_2.

Residual resistivity shows a maximum near the critical pressure, indicating strong electronic correlations.

Pressure influences magnetic and Kondo interactions, with hybridization playing a key role in the lower critical pressure of CePd_{2.02}Ge_{1.98}.

Abstract

The influence of pressure on the magnetically ordered CePd_{2.02}Ge_{1.98} has been investigated by a combined measurement of electrical resistivity, $\rho(T)$, and ac-calorimetry, C(T), for temperatures in the range 0.3 K<T<10 K and pressures, p, up to 22 GPa. Simultaneously CePd_2Ge_2 has been examined by $\rho(T)$ down to 40 mK. In CePd_{2.02}Ge_{1.98} and CePd_2Ge_2 the magnetic order is suppressed at a critical pressure p_c=11.0 GPa and p_c=13.8 GPa, respectively. In the case of CePd_{2.02}Ge_{1.98} not only the temperature coefficient of $\rho(T)$, A, indicates the loss of magnetic order but also the ac-signal $1/V_{ac}\propto C/T$ 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 (T,p) phase diagram and the A(p)-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 (T,V) phase diagram of CePd_2Ge_2 combined with that of CePd_2Si_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 CePd_{2.02}Ge_{1.98} is caused by an enhanced hybridization between 4f and conduction electrons.