Valence fluctuation and Kondo effect in noncubic Ce-transition metal compounds (invited)

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Abstract
In the compounds between cerium and transition metals, with an almost filled d band, the electronegativity difference between the constituents can lead to a position of the Fermi level compared to the 4f state which strongly depends on the stoichiometry. The following states of cerium are then expected: magnetic 3+state, 3+state with Kondo effect, and intermediate valence state. The various noncubic compounds of the Ce‐Ni and Ce‐Pt systems, which are presented in this paper, are very interesting because all these Ce states are observed. The interest of these alloys is enhanced because of their low symmetry which allows one to observe the anisotropic effects resulting from the hybridization of the 4f state with the conduction band; these properties cannot be observed in the cubic compounds such as CeSn3, CePd3, CeAl2. Because of the large difference of behavior between the isomorphous equiatomic CeNi and CePt compounds, a continuous evolution from a Ce3+ magnetic state to an intermediate valence state is observed in the CeNixPt1−x pseudobinary compounds. These compounds are among the best examples of a ferromagnetic dense Kondo system in which the variation of the Curie temperature TC and of the Kondo temperature TK as a function of the Ni content are similar to those predicted in the Kondo lattice model when ‖Γn(EF)‖ increases (Γ is the negative coupling constant between the 4f shell and the conduction band).