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Calorimetric and transport investigations of CePd2+xGe2-x(x=0 and 0.02) up to 22 Gpa

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The influence of pressure on the magnetically ordered CePd2.02Ge1.98 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, CePd2Ge2 has been examined by rho(T) down to 40 mK. In CePd2.02Ge1.98 and CePd2Ge2 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 CePd2.02Ge1.98 the temperature coefficient A of rho(T) not only indicates the loss of magnetic order but also the ac signal 1/V(ac)proportional toC/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 CePd2Ge2 combined with that of CePd2Si2 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 CePd2.02Ge1.98 is caused by an enhanced hybridization between 4f and conduction electrons.

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