Kondo lattice compounds

YbPdSb. Transport, bulk magnetic and caloric measurements (Le Bras et al. 1995, Suzuki et al. 1995, Bonville et al. 1997) clearly show that cubic YbPdSb is a Kondo-lattice compound. CEF interaction puts a Fg quartet lowest on which the Kondo coupling acts with a strength of T 7 K. 

Kitaoka et al. (1985a) showed with Si NMR (K(T), l/T ) that CeRu2Si2 is a non-magnetic Kondo-lattice compound below 7 = 12 K. They found that K depended on temperature, while did not. was about 30 at 4.2 K, and... 

Preliminary studies have also been made for the compound CeSuj that is a borderline case between a mixed-valent compound and a Kondo lattice compound (see sect. 4). MAQO have been observed for the c, C44 and (cn — Cyj) modes (Niksch et al. 1985, Suzuki et al. 1987a). Because the experiments were performed for r > 1 K only small Fermi surface pieces have been observed with normal electron masses. Heavy masses observed by conventional de Haas-van Alphen experiments (Johannsen et al 1984) have not be detected so far. As in the case of LaBg the — Cj2 mode also exhibits for CeSnj the rotational invariance phenomenon (Suzuki et al. 1987a). 

Recently MAQO experiments have also been performed for the Kondo lattice compound CePbj, see Niki et al. (1987). Figure 43 shows relative velocity changes for the c - Cj2 mode for B k in the temperature range between 0.38 K to 1.7 K. For magnetic fields from 18-23 T a clear MAQO with frequency F = 617 T is observed with an effective mass m lm = 43. More extensive experiments have to be performed in order to determine the Fermi surface geometry. The complicated B-T phase diagram will be discussed in sect. 4. 

There is a big difference in f-electron character between the Kondo regime and the valence-fluctuation regime. One may be tempted to think that the 4f electrons in a Kondo lattice compound with a large value of Tk are itinerant. This seems to be true, as shown later in detail for CeSns and CeNi or CeRu2Si2. 

The rare earth hexaborides RBg crystallize in the cubic (CaBe type) structure which possesses a CsCl type arrangement of R atoms and Be octahedra. Figure 7 shows the crystal structure of RBe and its simple cubic Brillouin zone. LaBe is a reference non-f compound. CeBg is a typical Kondo-lattice compound undergoing two magnetic ordering... 

Rare earth monopnictides RX possess the NaCl type crystal structure. The primitive cell contains one molecule of RX. Figure 45 shows the crystal structure and its Brillouin zone. Especially the CeX compounds, in which X stands for N, P, As, Sb and Bi, have attracted a particular interest because of various anomalous magnetic and transport properties (Kasuya et al, 1987). LaX is expected to be a semimetal with a small and equal number of electrons and holes. A similar semimetallic character is observed in CeX, except CeN. CeX is a Kondo-lattice compound, having anomalous magnetic properties at low temperatures. Even though the carrier number is small, the Kondo effect is strong and the... 

The large cyclotron mass of 80mo is detected in the non-magnetic Kondo-lattice compound CeCug. It is, however, not clear whether the 4f-electron character of CeCug is itinerant or localized. 

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