Kondo anomalies electrical resistivity

The interaction between impurity ions with partially filled d or f electron shells and the conduction electrons of a metallic host can lead to variations in certain physical properties with temperature and magnetic field which have come to be associated with the Kondo effect . In zero magnetic field, these temperature-dependent anomalies in the physical properties scale with a characteristic temperature Tk, the so-called Kondo temperature, above which the matrix-impurity system behaves magnetically and below which the matrix-impurity system behaves nonmagnetically. The physical properties which exhibit anomalies attributable to the Kondo effect include the electrical resistivity, magnetic susceptibility, thermoelectric power, specific heat and, in systems where appropriate, superconducting properties such as the critical temperature and the jump in specific heat which occurs at T. ... 

The reader is cautioned to observe, however, that existing theories for the various physical properties of Kondo systems do not provide a self-consistent definition for the characteristic temperature as defined by the temperatures of the typically broad anomalies in the thermoelectric power, electrical resistivity, heat capacity and magnetic susceptibility. Thus the values of the characteristic temperature inferred from different measurements may differ by as much as an order of magnitude. 

As mentioned in the Introduction (section 1), the electrical resistivity, specific heat, magnetic susceptibility and thermoelectric power anomalies of concentrated lanthanide Kondo systems are qualitatively similar to those found in the dilute lanthanide systems discussed previously. However the importance of the concentrated systems is that they provide a totally new view of Kondo-like phenomena. Lattice constant. X-ray photoemission (XPS) and Mossbauer isomer shift measurements indicate a strong correlation between systems that exhibit Kondo-like anomalies and systems in which the lanthanide ion has a mixed or intermediate valence. By mixed valence we mean that there are two 4f electron configurations accessible to each rare earth ion (e.g., Ce -Ce, Eu -Eu ", Yb -Yb ). Phenomenologically the traditional... 

The compounds YbC2, YbB4, Yblns, and YbCua (Gschneidner, 1961 Klaasse et al., 1973 Fisk et al., 1972 Sales, 1974) exhibit one or more anomalies associated with the Kondo effect. However, with the exception of a minimum at 40K in the electrical resistivity of YbC2 (Sales, 1974), the three compounds discussed previously typify the anomalies found in Yb systems. 

In order to clarify the origins of anomaly in the compression curve of CeAl2, the electrical resistance of CeAl2 was measured up to 23 GPa at room temperature using diamond-anvil cell under quasi-hydrostatic condition. According to the result obtained by cubic-anvil-type pressure device, the p P) increases with increasing pressure up to 5.5 GPa, and then decreases as shown in Figure 19B. The maximum is explained to be due to the Kondo effect, where tiie Kondo temperature Tr (which is around 6 K at ambient pressure) increases with pressure and then reaches room temperature around 5.5 GPa, that is, the pressure-induced crossover occurs in the vicinity of 5.5 GPa at room temperature. 

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