Samarium and europium intermediate valence compounds

The spin-orbit splitting of the Sm ion is the smallest of all the lanthanide ground state configurations. The transition of the 4f configuration is at 

Hirst (1970, 1975) has discussed the conditions under which the intra-ionic excitations remain sharp even though the compound is close to a configuration instability, or crossover, the condition being that 

Whilst no magnetic scattering has been identified in the mixed valence phase of SmS, it has been seen in Sm 25S by Mook et al. (1978) who observed a very broad peak with a FWHM of 15 meV at 30 meV. The addition of yttrium has a similar effect to that of pressure in contracting the lattice. At this composition, the valence changes with temperature from 2.3 to 2.45 at about 200 K (Weber et al. 1989). This means that the compound is at a configuration crossover with the f level effectively pinned at the Fermi level Ep, — Ep-i = p) such that the ground state consists of a hybridised mixture of the two configurations. The valence is then determined by thermodynamic considerations in which the ionic excitation 

Coefficients of radial integrals in the neutron scattering 1,2,.. ., 6 transitions. cross-sections of Sm , / = 0 / = 

Structure of each configuration plays an important role (Wohlleben 1984). For instance, at high temperatures (k the valence adjusts to maximise the 

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