154 research outputs found
A teaser made simple: a didactic measurement of the spectral answer of a human-eye-calibrated lux meter
A simple didactic experiment has been designed and realized, in order to illustrate to undergraduate students in scientific faculties some basic concepts lying behind the fundamentals of geometrical optics. The spectral response of a human-eye-calibrated lux meter was measured using a very trivial experimental arrangement. The white light of a halogen lamp was decomposed into its spectral components through a diffraction grating, so that collecting the radiation at different dispersion angles allowed one to measure the intensity as a function of wavelength. The experiment can be used to effectively illustrate the concepts of spectral distribution, the radiometry versus photometry conversion and photopic response, and the famous historical experience by Herschel on the 'temperature of colours'
Influence of exchange bias coupling on the single-crystalline FeMn ultrathin film
Polarization dependent x-ray photoemission electron microscopy was used to investigate the influence of the exchange bias coupling on the disordered ultrathin single-crystalline fcc Fe50 Mn50. We find that the critical thickness of the FeMn film, where the antiferromagnetic (AF) order is formed, varies with changing the magnetization direction of the ferromagnetic (FM) layer from out-of-plane to in-plane. Surface magneto-optical Kerr effect measurements (SMOKE) further manifest the shift of the critical thickness with alternating the exchange bias coupling. It indicates that the spin structure of the FeMn layer near the FM layer is modified by the presence of exchange bias coupling and the properties of the coupling. Our results provide direct experimental evidence that the AF spin structure at the interface between the FM and AF layers is strongly influenced by the exchange bias coupling. © 2005 American Institute of Physics.published_or_final_versio
Electronic Structure of CeFeAsO1-xFx (x=0, 0.11/x=0.12) compounds
We report an extensive study on the intrinsic bulk electronic structure of
the high-temperature superconductor CeFeAsO0.89F0.11 and its parent compound
CeFeAsO by soft and hard x-ray photoemission, x-ray absorption and soft-x-ray
emission spectroscopies. The complementary surface/bulk probing depth, and the
elemental and chemical sensitivity of these techniques allows resolving the
intrinsic electronic structure of each element and correlating it with the
local structure, which has been probed by extended-x-ray absorption fine
structure spectroscopy. The measurements indicate a predominant 4f1 (i.e. Ce3+)
initial state configuration for Cerium and an effective valence-band-to-4f
charge-transfer screening of the core hole. The spectra also reveal the
presence of a small Ce f0 initial state configuration, which we assign to the
occurrence of an intermediate valence state. The data reveal a reasonably good
agreement with the partial density of states as obtained in standard density
functional calculations over a large energy range. Implications for the
electronic structure of these materials are discussed.Comment: Accepted for publication in Phys. Rev.
Unexpectedly large electron correlation measured in Auger spectra of ferromagnetic iron thin films: orbital-selected Coulomb and exchange contributions
A set of electron-correlation energies as large as 10 eV have been measured
for a magnetic 2ML Fefilm deposited on Ag(001). By exploiting the spin
selectivity in angle-resolved Auger-photoelectroncoincidence spectroscopy and
the Cini-Sawatzky theory, the core-valence-valence Auger spectrumof a
spin-polarized system have been resolved: correlation energies have been
determined for eachindividual combination of the two holes created in the four
sub-bands involved in the decay: majorityand minority spin, as well asegandt2g.
The energy difference between final states with paralleland antiparallel spin
of the two emitted electrons is ascribed to the spin-flip energy for the final
ionstate, thus disentangling the contributions of Coulomb and exchange
interactions.Comment: 5 pages, 2 figures, 1 tabl
Identification of hidden orbital contributions in the La_{0.65} Sr_{0.35} MnO_{3} valence band
Hybridization of electronic states and orbital symmetry in transition metal oxides are generally considered key ingredients in the description of both their electronic and magnetic properties. In the prototypical case of La_{0.65} Sr_{0.35} MnO_{3} (LSMO), a landmark system for spintronics applications, a description based solely on Mn 3d and O 2p electronic states is reductive. We thus analyzed elemental and orbital distributions in the LSMO valence band through a comparison between density functional theory calculations and experimental photoelectron spectra in a photon energy range from soft to hard x rays. We reveal a number of hidden contributions, arising specifically from La 5p, Mn 4s, O 2s orbitals, considered negligible in previous analyses; our results demonstrate that all these contributions are significant for a correct description of the valence band of LSMO and of transition metal oxides in general
Valence band electronic structure of V2O3: identification of V and O bands
We present a comprehensive study of the photon energy dependence of the
valence band photoemission yield in the prototype Mott-Hubbard oxide V2O3. The
analysis of our experimental results, covering an extended photon energy range
(20-6000 eV) and combined with GW calculations, allow us to identify the nature
of the orbitals contributing to the total spectral weight at different binding
energies, and in particular to locate the V 4s at about 8 eV binding energy.
From this comparative analysis we can conclude that the intensity of the
quasiparticle photoemission peak, observed close to the Fermi level in the
paramagnetic metallic phase upon increasing photon energy, does not have a
significant correlation with the intensity variation of the O 2p and V 3d
yield, thus confirming that bulk sensitivity is an essential requirement for
the detection of this coherent low energy excitation
Depth dependence of itinerant character in Mn-substituted Sr3Ru2O7
We present a core-level photoemission study of Sr3(Ru 1-xMnx)2O7, in which we
monitor the evolution of the Ru-3d fine structure versus Mn substitution and
probing depth. In both Ru 3d3/2 and 3d5/2 core levels we observe a clear
suppression of the metallic features, i.e. the screened peaks, implying a sharp
transition from itinerant to localized character already at low Mn
concentrations. The comparison between soft and hard x-ray photoemission, which
provides tunable depth sensitivity, reveals that the degree of
localized/metallic character for Ru is different at the surface than in the
bulk.Comment: 10 pages, 4 figures, 1 tabl
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