Resonant KLL Auger spectra of ferromagnetic metals Fe and Co

Complete text of publication follows. Resonant KLL Auger spectra of 3d transition metals contain important information on the nature of the Auger process including solid state effects due to changes in the electronic structure local to the initial state core hole. Tuning the energy of the monochromatic exciting photons across the K-absorption edge, features characteristic to resonant phenomena can be reflected in the spectra. In the case of the resonantly photoexcited KLL Auger spectra induced from Cu and Ni metals, the spectral shapes have been successfully described using the single step model based on the resonant scattering theory for describing the Auger process. The 4p partial density of unoccupied electronic states was derived from a cluster molecular orbital model, while a realistic correction of the experimental spectra was applied for contributions of electrons scattered inelastically within the samples. As a function of exciting photon energy, a linear dispersion of the energy position of the peak maximum and a significant distortion of the peak shape was found, indicating the presence of the Auger Resonant Raman effect. For observing resonantly photoexcited KLL Auger transitions in 3d metals and study- ing threshold dynamics of Auger satellites the Tunable High Energy XPS (THE XPS) facility at the BW2 beamline of HASYLAB provides optimum conditions. KL2L3 Auger spectra of polycrystalline Fe and Co were measured using the THE-XPS instrument with the SES-200 analyser with an energy resolution of 0.2 eV. For electron energies exceeding 5 keV, a proper positive bias voltage was applied on the sample. Energy calibration of the energy scale was performed by using reference data for Cu L3VV and Au M5N67N67 Auger lines as well as for Cu 2p photolines excited by Kα X-rays photoinduced internally in the calibrating Cu sample. Using Si (220) (Fe) and Si (111) (Co) monochromators ensuring a photon beam energy width of 1.1 eV, KLL spectra were obtained down to 3 eV (Fe) and 2 eV (Co) photon energies below K-threshold. Fig. 1 shows the Fe KLL spectra recorded at threshold and sub-threshold excitations, indicating the signature of the Auger Resonant Raman process. Similar results were obtained for the resonant Co KLL spectra. This work was supported by the IHP-Contract HPRI-CT-199-0040/2001-00140 of the European Commission and by the Hungarian Project OTKA T038016. (author)