Unexpectedly large electron correlation measured in Auger spectra of ferromagnetic iron thin films: orbital-selected Coulomb and exchange contributions

Abstract

A set of electron-correlation energies as large as 10 eV have been measured for a magnetic 2ML Fe film deposited on Ag(001). By exploiting the spin selectivity in angle-resolved Auger-photoelectron coincidence spectroscopy and the Cini-Sawatzky theory, the core-valence-valence Auger spectrum of a spin-polarized system have been resolved: correlation energies have been determined for each individual combination of the two holes created in the four sub-bands involved in the decay: majority and minority spin, as well as eg and t2g. The energy difference between final states with parallel and antiparallel spin of the two emitted electrons is ascribed to the spin-flip energy for the final ion state, thus disentangling the contributions of Coulomb and exchange interactions.

Electron correlation effects in the exchange coupling at the Fe/CoO/Ag(001) ferro-/antiferro-magnetic interface

“…In general, the relative weight of antiparallel spin versus parallel spin emission can be expressed as a function of |∆m| = |m 1 − m 2 |, where m 1 and m 2 are the m values of the two emitted electrons; the higher |∆m|, the higher the probability of PS emission [21]. In this experiment, for Auger electrons emitted In analogy to previous AR-APECS experiment [24,28], the analyzers pairs selecting photoelectrons emitted close to the polarization vector will be termed as antiparallel spin configuration (AS) , while pairs with the photoelectron far from will be termed parallel spin configuration (PS).…”

“…The surface quality was monitored by RHEED, photoemission spectroscopy and the X-ray absorption at the Fe L 23 edge. The Fe thickness was estimated by using evaporation conditions (time and rate) identical to those used to achieve two complete RHEED oscillations [32] in a previous experiment performed on Fe/Ag(001) with the same experimental setup [28].…”

“…3. In the upper panel, the Fe 3p high resolution (0.2 eV) XPS spectrum of the Fe/CoO interface is compared with the one measured for the Fe/Ag interface [28], after alignment and normalization to their maximum intensity; their difference, shown by the black continuous line and which is interpreted as an evidence for the formation of iron-oxygen bonds at the Fe/CoO interface, provides an estimate of the contribution to the Fe 3p peak intensity due to iron atoms bonded to oxygen, which results less than 10% of the contribution ascribable to metal atoms. In the lower panel of Fig.…”

“…Furthermore, when the emission angle of the two electrons is taken into account, APECS becomes sensitive to the total spin of the two-hole final state [21,22]. With the discovery of the dichroic effects in angle resolved APECS (DEAR-APECS), it has been possible to isolate, in the Auger spectrum of FM and AFM thin films, the individual contributions of specific hole-hole pairing originating from spin polarized bands, allowing a deeper insight into the local magnetic structure of these systems [23,24,25,26,27,28].…”

“…Fe/CoO [16], are compared with results obtained for a system where it is not present, i.e. Fe/Ag, which is assumed as a reference [28]. The paper is organized as it follows: section 2 introduces the experimental methods, the experimental results are presented and discussed in section 3 and section 4 is devoted to the conclusions.…”