Calorimetric and transport investigations ofCePd2+xGe2−x

H. Wilhelm

¹

,

D. Jaccard²

Abstract

The influence of pressure on the magnetically ordered CePd2.02Ge1.98 has been investigated by a combined measurement of electrical resistivity, ρ(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 ρ(T ) down to 40 mK. In CePd2.02Ge1.98 and CePd2Ge2 the magnetic order is suppressed at a critical pressure pc = 11.0 GPa and pc = 13.8 GPa, respectively. In the case of CePd2.02Ge1.98 not only the temperature coefficient of ρ(T ), A, indicates the loss of magnetic order but also the ac-signal 1/Vac ∝ 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 pc. 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 pc-value of CePd2.02Ge1.98 is caused by an enhanced hybridization between 4f and conduction electrons.

Multiprobe experiments under high pressure: Resistivity, magnetic susceptibility, heat capacity, and thermopower measurements around 5 GPa

“…The price one has to pay is the need to take into account of different constraints of several setups, which means a higher degree of complexity and that the ideal conditions for a single property may not be completely achieved. Some of the past examples of multiprobe experiments, under pressure, are in situ x-ray diffraction and electrical resistance measurements, 6 calorimetric, and transport investigations 7 and more recently, electronic, and magnetothermal transport measurements, 1 etc. Here, we report the setup and results of a multiprobe experiment using a single Bridgman-anvil pressure cell and a liquid medium.…”

Electrical resistivity study of CeZn11: Magnetic field and pressure phase diagram up to 5 GPa

“…A similar influence of the CEF levels on the electrical resistivity can be observed in many other cerium based compounds. [29][30][31][32][33][34][35][36][37][38][39][40][41] The two anomalies we observe are expected to merge under pressure with the increase of the Kondo effect 42 and indeed, at a qualitative level, this is observed in Fig. 1(b) as the pressure is increased.…”

“…This value for CeZn 11 can be compared to Ce 3 Pt 4 In 13 ( d|J ex | dp ≈ 8.4 meV/GPa), which orders antiferromagnetically below 0.95 K. 38 It would be interesting to compare these values to other cerium compounds, especially members of the CeT 2 (Si,Ge) 2 (T = Cu,Pd,Au). [31][32][33][34][35] The knowledge of the pressure dependence of J ex will be used later to estimate the variation of the magnetic ordering temperature T O 1 (p). We note that fitting down to 5 K with 1 as a free parameter gave essentially the same estimate of the variation of the magnetic ordering temperature T O 1 (p), and values for 1 between 14 and 18 K. However, as already mentioned, the data are not well reproduced at low temperatures.…”

Correlated thermoelectrics

“…The experimental results show that 4f systems with similar thermopowers exhibit similarities in other thermodynamic [44] and transport [45,46,47] properties, and there is an obvious correlation between the shape of α(T ) and the magnetic character of the 4f ions. The thermopower measurements [48] provide a simple and sensitive tool for characterizing the magnetic state of a 4f ion in a given metallic matrix: the shape of α(T ) changes from the (a)-type in the case of magnetic Ce (Yb) ions with stable f 1 (4f 13 ) configuration to the (d)-type for non-magnetic Ce (Yb) ions which fluctuate between the 4f 1 (4f 13 ) and 4f 0 (4f 14 ) configurations.…”