4f Occupation and hybridization from M-shell excitations in Rare-Earth materials

Abstract

M-shell excitations in Rare-Earth (RE) materials were studied using synchrotron radiation and total electron yield detection in UHV. In mixed-valent compounds of the heavy RE's (Sm, Eu, Tm), the M_4,5 spectra are identified as superpositions of quasi-atomic 3d⁹4fⁿ⁺¹ multiplet structures, providing quantitative information on the mean valence ν̅(4f occupation) of the RE ions, even in highly dilute systems. The method employed in deriving quantitative values for ν̅ is described in some detail. Effects of 4f/valence-band hybridization on the M_4,5 spectra are investigated for Ce systems: the 3d⁹4f² multiplet structure seen in γ-like Ce compounds is found to collapse in α-like systems, where satellites at about 5 eV higher energies are additionally observed. The method is also applied to dilute Ce systems, such as Ce in a Pd matrix, which is found to be α-like. In addition, M₃-edge spectra are presented for a series of Ce compounds, and their relation to L₃-edge spectra is discussed.