Origin of the high-binding-energy structure in the 3dcore-level spectra of divalent Eu compounds

Abstract

Brief Reports are accounts of completed research which, while meeting the usual Physical Review standards of scientific quality, do not warrant regular articles. A Brief Report may be no longer than four printed pages and must be accompanied by an abstract. The same publication schedule as for regular articles is followed, and page proofs are sent to authors.The high-binding-energy structure in the Eu 3d core-level x-ray photoelectron spectra of divalent Eu compounds, which has been ascribed as the "shakeup" satellite, is shown to be due to the multiplet structure of 3d4f i (bar denotes a hole) final-state configuration. Hence, the apparent inconsistency between this so-called high-energy probe and low-energy probes for the valence of these Eu compounds is resolved.Rare-earth metals and their compounds have been the subject of extensive study because of the valence Auctuation phenomena' and heavy fermion properties, which originate from the interaction between highly correlated 4f electrons and delocalized conduction electrons. Corelevel x-ray photoelectron spectroscopy (XPS) has been very valuable in studying electronic structures of these compounds. Core-level spectra can be usually understood by the following Anderson impurity Hamiltonian including the Coulomb interaction between the core hole and 4f electrons: ' XH = g f Ftp, +"tp"de+[a& -U&, (1 n, )]q&+ -pt v= 1 + f [V(e)tp" tp"+ V(e)*tp, +, tp, ]dE + UJJ g~n~n E+~n P)V where e describes the energy of the conduction-band state, e& is the energy of the 4f level, and E, describes the energy of a core level. The 4f level has N&-fold degeneracy, whose quantum numbers are denoted by p, v. The hopping between the 4f level and the conduction state is described by V(e) and the Coulomb interaction between 4f electrons is given by UI&, where in the simple model multiplet effects are neglected. U&, is the Coulomb interaction between a core hole and an f electron. Thus while the~f")and~f" + ' ) states are nearly degenerate in energy in the initial state, they have an energy separation of U&, in the final state of photoemission, because the energy of the~f ") state is pulled down by the amount n U&, (n is the number of f electrons) by the core hole created in photoionization.This gives rise to the satellite structure in the deep core-level XPS spectra, whose intensity depends on the strength of V(e) and the energy position of e&. Therefore, by analyzing deep core-level XPS spectra, we can get information of the valence electronic structure. For this purpose 3d core-level spectra usually used because 4d core-level XPS shows very complicated multiplet structures due to the strong interaction between the 4d hole and unfilled 4f shell (they have the same principle quantum number n =4). Many Ce compounds and several Yb compounds have been studied by the core-level XPS technique, and they are shown to be consistent with physical properties measured by so-called low-energy probe techniques such as Mossbauer isomer shift and the magnetic susceptibility. ' However, for some Eu co...

Chemical stability of the magnetic oxide EuO directly on silicon observed by hard x-ray photoemission spectroscopy

“…Both energy splitting and intensity ratios compare well with previous reports of calculated and measured multiplet spectra of divalent Eu compounds. 28,30 Moving to the oxygen-rich EuO compound (ii) in Fig. 5(c), we observe prominent double-peak structures in the 3d 5/2 (3d 3/2 ) regions, which are separated by 10.45 eV (10.90 eV).…”

“…5(e). 28 We identify a satellite peak in the high binding energy region of the Eu 3d 5/2 and 3d 3/2 multiplet, respectively, which is separated by 7.8 eV (6.3 eV) from the 3d 5/2 (3d 3/2 ) main peak. These main peak/satellite doublets are assigned to the divalent Eu 2+ multiplet of the 3d 9 4f 7 final state.…”

“…For Eu 2+ peak fitting, a multiplet fine structure was employed in accordance with theoretical calculations in Ref. 28. The result of the fitting procedure is summarized in Table I .…”

“…5(e). 28,30 For a depth-sensitive analysis of the 3d core levels, the energy and angle-dependent information depths are calculated as D For the quantitative analysis of the Eu 3d core levels, we performed the curve fitting of the Eu 2+ 3d multiplet fine structure in accordance with Ref. 28 using convoluted Gaussian-Lorentzian lines with consistent intensity ratios, peak widths and energy differences.…”

Heteroepitaxy and ferromagnetism of EuO/MgO (001): A route towards combined spin- and symmetry-filter tunneling

“…Figure 3 depicts the Eu 4d and 3d 3/2 core-level spectra recorded at a photon energy of hν = 6 keV and T = 33 K. Both spectra show well-resolved final-state multiplets, which agree very well with photoemission multiplets of Eu 2+ ions from experimental studies of divalent Eu compounds 15,16 and theoretical multiplet calculations. 23,24 At the high-binding-energy side, smaller spectral contributions are observable, which are part of the complex Eu 2+ final-state multiplet and do not indicate any different EuO phases, e.g., Eu 3+ ions.…”