Intermediate-valence state of the Sm and Eu in SmB 6 and EuCu 2 Si 2 : neutron spectroscopy data and analysis.

Magnetic neutron scattering data for Sm (SmB6 , Sm(Y)S) and Eu (EuCu2 Si2-x Ge x ) intermediate-valence compounds have been analysed in terms of a generalized model of the intermediate-radius exciton. Special attention is paid to the correlation between the average ion's valence and parameters of the low-energy excitation in the neutron spectra, such as the resonance mode, including its magnetic form factor. Along with specific features of the formation of the intermediate-valence state for Sm and Eu ions, common physical mechanisms have been revealed for systems based on these elements from the middle of the rare-earth series. A consistent description of the existing experimental data has been obtained by using the concept of a loosely bound hole for the Eu f-electron shell in the intermediate-valence state, in analogy with the previously established loosely bound electron model for the Sm ion.