Heavy fermion CeAlj

Kondo-like resistivities can also be observed in concentrated Kondo compounds. Typical examples are CeAlj (Buschow et al. 1971), CeAl2 (Buschow et al. 1969), CeCu2Si2, (Steglich et al. 1985) and CeSnj (Gschneidner et al. 1985). A characteristic property is the low-temperature specific heat or its y-value, y = CIT, which has very large values of the order of 1 J Mol K (see table 5). This large value for y, expressed in electron density of states or effective masses m Im (of the order of 200) have led to the name of heavy-fermion compounds (Stewart 1984). 

Characteristic differences arise in the electronic excitation spectrum of heavy-fermion magnets in the different regimes. For a magnetic state with well localized moments and only moderate enhancement of y (i.e., of order 0.1 J mol ) as in CeAlj, the following picture has been proposed (Doniach 1977, Nozieres 1985) starting from band electrons and ionic f-states, the quasiparticle renormalizations stop when spin order of somewhat renormalized moments occurs. The corresponding RKKY interactions with energy scale are mediated by... 

Ce intermetallic compounds, in which the local moment of the 4f electron is quenched and in which the volume of the Ce ion is similar to that of y (a)-Ce are called y (a)-type materials (e.g. CePds). The first published BIS spectrum of an a-type material was the spectrum of CePdj, by Baer et al. (1981) shown in fig. 17. Also shown are data for y-Ce and for the heavy-fermion compounds CeAlj and CeSns- In these spectra the 4f final state can be easily identified because it appears with similar energy and shape as in y-Ce. The BIS spectrum of CePdj also contains a 4f signature, shifted however from p by about 1.1 eV compared to y-Ce. In addition it shows two more peaks at 0.45 and 2.25 eV. The peak at 0.45 eV above Ey, whose... 

Fig. 20. Wide scan single crystal spectra (except CeAlj and CeSij) for several Ce heavy fermions with ranging fton 1 Kto 400K. Data taken at 20K, 120eV and 90meV resolution. Note the lack of scaling of the dfj/j peak with Ty. TWo different directions are shown for CeBei3 with vastly different spectra.

---