Kondo-lattice system

The groimd-state properties of Kondo-lattice systems, for example, are expected to be very sensitive to external pressure. The latter may modify the strength of the exchange interaction J between the localized 4f and the conduction electrons and thereby the competition between the intersite (RKKY) and intrasite (Kondo) interactions. The balance between these effects has been theoretically described by Doniach (1977) for a magnetic phase diagram depending on the exchange parameter J. 

In what might be described as the contemporary era of rare earths, much emphasis has been placed on the use of lanthanides as local-moment impurities, for example in studies of the co-existence of superconductivity and magnetism and in spin-glass phenomena. Also the band-like characteristics of the 4f moment of Ce has been the cornerstone of an intense effort in understanding valence fluctuation effects, Kondo-lattice systems, and heavy fermion superconductivity. 

Cerium and uranium materials related to concentrated Kondo lattice systems for which the thermal... 

Striking behavior has been observed for CeB6, SmBe, and YbBe. CeBe was first pointed out by Kasuya and others to be a heavy electron system. s jg so-called Kondo lattice system with the Kondo effect from the localized f-electrons and conduction electrons playing a large role in the determination of the physical properties. Complex phases have been reported and quadrupole and octupole coupling are also indicated to be effective. SmBe exhibits valence fluctuation and is a Kondo insulator with a gap temperature of A = 27 K. YbBe has been reported to exhibit valence fluctuation also. 

Steglich et al. 1980). Therefore, the Kondo-lattice system is called a heavy-electron or heavy-Fermion system. 

The RAI2 rare earth compounds possess the cubic Laves-phase structure, which is shown in fig. 58. CeAl2 provides a good example of a Kondo-lattice system with the Fy ground state and an incommensurate sinusoidally modulated antiferromagnetic structure below 3.8 K (Barbara et al. 1979), as shown in table 14. 

Magnetic, calorimetric and transport measurements characterize CeCu2Ge2 as a Kondo-lattice system which orders antiferromagnetically below = 4.15(5) K. (de Boer et al. 1987). 

Tokura, Y., Urushibara, Y, Moritomo, Y, Arima, T., Asamitsu, A., Kido, G., and Furukawa, N. Giant Magnetolransport phenomena in filhng-controUed Kondo lattice system Lai cSr cMn03. J. Phys. Soc. Jpn. 1994, 63,3931-3935. 

This indicates a modulated spin structure. The maximum is around 300 T corresponding to a moment of 1.5 /in quite in contrast to the low moment of NpSnj. From high-pressure data it was concluded that NpSuj is a Kondo lattice system. Kondo behavior may also be present in Npln3 as suggested by recent resistivity data (Gal et al. 1992). 

Shell structure, relativistic and electron correlation effects play an important role for the electronic structure of lanthanide and actinide systems. The importance and the magnitude of these effects have been examplified for the atoms Ce and Th, and the contributions of the Ce 4f and Th 5f shell to chemical bonding have been reviewed for the monoxides CeO and ThO, respectively. Currently quantitatively correct results for lanthanides and actinides can only be obtained from ab initio calculations for the easiest cases, e.g., small systems (atoms, diatomics containing one f element) with a possibly small number of unpaired f electrons and/or problems related only to configurations with the same f occupation number. In other cases ab initio quantum chemistry can at least help to interprete experimental findings. As an example organometallic cerium sandwich complexes such as cerocene were discussed, which may be considered to be molecular analogues of cerium(in)-based Kondo lattice systems. 

---