268 research outputs found
Magnetic asymmetry in photoemission from Fe(100) with linearly polarized synchrotron radiation
No full textWe have measured partially angle-integrated photoemission with linearly polarized undulator radiation on the valence band and on the 3p and 3s core levels of iron in an Fe(100) single crystal. A large asymmetry is measured for 3p core levels when reversing the magnetization direction perpendicular to the photoemission plane. A smaller but clear asymmetry is also measured in the valence (3d) band spectrum, and no asymmetry is measured for the 3s core levels. The results are explained by the transverse spin polarization of the near-normal-emission photoelectrons which is induced by the light p polarization and by spin-orbit interaction in the initial state. From the line-shape change of the 3p core level as a function of magnetization reversal the fine structure of the 3p multiplet is derived. This effect provides a very efficient diagnostic of the surface magnetization direction allowing to measure magnetic ordering at surfaces similarly to the Kerr effect, but in a chemically specific and intrinsically surface sensitive way as shown by examples on ferromagnetically coupled and antiferromagnetically coupled Fe/Cr interfaces
Costruire l’impalcatura del proprio futuro: storie postcoloniali di voci migranti italiane.
No full textIl saggio considera la scrittura della migrazione in Italia, in particolare quella femminile e in rapporto all'eredità coloniale e alla complessa ridefinizione postcoloniale contemporanea
Surface vs. bulk magnetic moments from photoemission dichroism
No full textThe value of the surface spin magnetic moment of Fe(100) is obtained by measuring the energy spread of the photoemission dichroism spectra of Fe3p core levels from bulk and surface. The bulk and surface signals have been resolved exploiting the photoemission diffraction effects in a linear magnetic dichroism of the angular distribution (LMDAD) experiment with soft X-rays. The LMDAD lineshape and energy width of the bulk contribution has been independently obtained from angular and from photon energy dependent experiments: it provides a gauge for determining the magnetic moment of the surface Fe3p atoms in the hypothesis of a linear dependance between energy width of dichroism and local spin magnetic moment
THERMAL EVOLUTION FROM A PRECURSOR TO THE Y-BA-CU-O SUPERCONDUCTOR - X-RAY ABSORPTION-SPECTROSCOPY STUDY AND APPLICATION TO THICK-FILM TECHNOLOGY
No full textThe local structure around Cu and Y atoms in a Y-Ba-Cu-O precursor prepared by spray pyrolysis was investigated by x-ray absorption spectroscopy. Near-edge and extended x-ray absorption fine structure analysis, together with powder diffraction measurements, give detailed information about structure and morphology of the precursor, as well as a clear picture of its thermal evolution towards the superconducting phase. Thick films prepared starting from this precursor are characterized. Their excellent properties exemplify possible applications of this material
LMDAD as a surface magnetometry
No full textLinear Magnetic Dichroism in the Angular Dependence (LMDAD) in â > 0 core level photoemission can be used as an atom-specific magnetometer. Its large dichroic signal is directly proportional to the surface magnetization and probes in a very efficient way the changes of magnetic moments as a function of the environmental conditions
Magnetic dichroism in the angular distribution of Fe 2p and 3p photoelectrons: Empirical support to Zeeman-like analysis
No full textWe report on the measurements and analysis of Fe 2p magnetic dichroism in the angular distribution of the photoelectrons from remanently magnetized Fe(100) surfaces with unpolarized, monochromatized, x rays of 1486 eV energy, and with linearly polarized synchrotron radiation of 800 eV energy. The analysis of the dichroic photoemission intensity in the two experiments verifies the applicability of the atomic photoionization model which provides a consistent understanding of the differences between photoemission experiments with unpolarized and linearly polarized radiation. A comparison of the Fe 2p and Fe 3p dichroism spectra allows us to discuss, on an empirical basis, the validity of a Zeeman-like interpretation of Fe 3p hole sublevels connected to the observed magnetic dichroism in photoemission
Spin filtering effect on secondary electrons crossing an iron overlayer
No full textSpin polarization (SP) measurements of the secondary electron yield from ferromagnetic interfaces is a sensitive probe of surface and interface magnetism. By exploiting the jumps of the total photoionization cross section in correspondence of the L-edge excitation in transition metals one introduces a chemical sensitivity in the SP via the enhancement of the secondary emission from a specific magnetic or non magnetic specie at the interface. The hÎ1⁄2-dependence of the SP in overlayer experiments allows to derive accurately the total and spin-dependent attenuation lengths for secondary electrons in non-magnetic and ferromagnetic materials
Linear Magnetic Dichroism in Directional Photoemission from Core Levels and Valence Bands
No full textThe need for new surface specific probes of magnetism is very high. The ideal surface magnetic probe should be selectively sensitive to surface, subsurface and interface layers, atom-specific and site specific, i.e. sensitive to the local environment of the excited atom, an should provide an absolute measure of the magnetic moment associated to the selected atoms. The field of surface magnetism has been opened by the application of spin-polarimetry to photoelectrons and to the secondary electron yield.[1] The measure of spin polarization (SP) of secondaries is intrinsically surface sensitive due to the short escape depth for low energy photoelectrons in ferromagnets, and can be understood semi-quantitatively.[2] The magnetic resolution of SP is high and can be used for imaging surface magnetic domains[3] and for studying the dynamics of surface magnetism with time resolution in the picosecond range in laser experiments,[4] or in the nanosecond range in synchrotron radiation experiments.[5] SP of secondaries probes the average magnetization and cannot be made atom-specific without independent knowledge on the atomic structure. [6] Spin Polarized Low Energy Electron Diffraction is very surface sensitive,[7] but it is limited to ordered surfaces, and is not atom specific. The magneto-optic Kerr effect [8] is not surface sensitive and can be applied only to the study of ferromagnetic order in monolayers on non magnetic substrates
Analysis of light energy distribution by multifocal intraocular lenses through an experimental optical model
No full textSuperconducting Thick-Films From a Y-Ba-Cu-O Precursor
No full textWe have prepared screen-printed films of the Y-Ba-Cu-O compound starting from a spray-pyrolysis
precursor powder. BeO ceramic substrates are confirmed to be inert with respect to the film up to
about 1000ºC. Electrical properties of oxygen annealed films are investigated, evidencing excellent
superconducting behaviour, both in terms of Tc(≃91K)
and Jc (>102 A.cm-2 at 77 K)
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