Kondo minima

It is well known that dilute magnetic alloys which have a Kondo minimum in the resistivity, also exhibit a giant thermopower anomaly. This anomaly was first treated theoretically by Kondo (1965) and later by Suhl and Wong (1967), Fischer (1967) and Maki (1969). 

The specific resistivity of ferromagnetic YbNiSn was investigated for a single crystal (Bonville et al. 1992). From these measurements it is evident that the specific resistivity is the highest in the c-direction (fig. 15), where the ferromagnetie moments lie. Also the Kondo minimum and the crystal electric field effects are pronounced in this direetion. 

The first study of (Ag, Au)Yb alloys was done by Boes et al. (1968), who observed that for Yb concentrations of less than 0.15 at.% in a Ag, Au host a Kondo minimum in the temperature dependence of the electrical resistivity was found in annealed alloys for Au concentrations between 10 and 40 at.%. However, the resistive behavior was also found to depend markedly on the details of the alloy heat treatment. 

Measurements of p T) for TiB2 by Williams et al. (9) from 4.2 to 300 K showed a resistivity minimum in the range 34-47 K. A normal resistivity term Pei.ph(r) could be extracted. It was well described by a Bloch-Griineisen expression varying as at low T and with Or = 720 K. The latter value seems reasonable, when compared with 0s see Table 1. The Kondo effect is caused by a spin-flip interaction between conduction electrons and localized magnetic moments of impurity atoms. Ni impurities are essential, but there are still several unsolved problems in the interpretation of the Kondo minimum in TiB2. 

Kondo J (1964) Resistance minimum in dilute magnetic alloys. Prog Theor Phys 32 37... 

Fig. 1. Ultraviolet light curves of beta Lyrae observed with the 0A0-2 (Kondo, McCluskey and Eaton 1976, An. Space Sci. , 41. 121). Note the deepening of the secondary minimum in the far-ultraviolet.

The CeNi2Sb2 compound was classified as Kondo system by Kaczmarska et al. (1993) from magnetic properties and resistivity measurements. The resistivity shows a maximum at 2.5 K and a minimum at 28 K (fig. 39). As reported by Skolozdraet al. (1994), it has aCurie-Weiss... 

Licorice contains approximately 1 to 7% of the compound glycyrrhizin (Kondo et al. 2007). Many commercial products are standardized to 12% glycyrrhizin, and the European Pharmacopoeia specifies that licorice root should contain a minimum of 4% glycyrrhizin (Council of Europe 2001). 

For instance, the value of b was found in the analysis given -by Okuno and Sakurai to be equal to — 8 X 10 in GdQ 4oCoo.6o- This value is virtually the same as the one that can be derived from the results shown for Lao 4oCoo go in fig- 67. A fit to their data made on the basis of eq. (67) is shown in fig. 74. The interesting point here is the fact that the resistivity minimum arises as a consequence of the magnetic term and the Ziman term, the Kondo-like behaviour observed in the low-temperature regime being of minor importance. 

Sugawara observed the first resistance minimum phenomenon due to a lanthanide solute in the dilute alloy system YCe. Following this discovery of the Kondo effect in the YCe system, numerous dilute and concentrated lanthanide metallic systems have been investigated over the past decade. Of the thirteen lanthanide ions with partially-filled 4f shells, Kondo-like behavior has been observed for Ce, Pr, Sm, Eu, Tm and Yb. 

Early work on dilute lanthanide systems was motivated by the vast experimental and theoretical effort that had been expended on understanding dilute magnetic 3d impurities in noble metal hosts. In 1965, Sugawara discovered a resistance minimum in the YCe system, providing the first evidence of Kondo behavior for a lanthanide solute. This led to the discovery of numerous lanthanide Kondo systems which exhibited anomalies in their physical properties qualitatively identical to those found in 3d Kondo systems. 

Fig. 11.14. Temperature of the Kondo resistance minimum depth of the resistance minimum dpmin, and logarithmic slope of the solute incremental resistivity -d(4p)/d(log T) for (Ag, Au)Yb alloys vs Au composition of the Ag, Au matrix from resistivity data of Talmor and Sierro (1975).

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. 

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