45 research outputs found
Electron correlation effects and magnetic ordering at the Gd(0001) surface
Effects of electron correlation on the electronic structure and magnetic
properties of the Gd(0001) surface are investigated using of the full-potential
linearized augmented plane wave implementation of correlated band theory
("LDA+U"). The use of LDA+U instead of LDA (local density approximation) total
energy calculations produces the correct ferromagnetic ground state for both
bulk Gd and the Gd surface. Surface strain relaxation leads to an 90 %
enhancement of the interlayer surface-to-bulk effective exchange coupling.
Application of a Landau-Ginzburg type theory yields a 30 % enhancement of the
Curie temperature at the surface, in very good agreement with the experiment.Comment: revised version: minor typos correcte
A Spin-Resolved Photoemission Study of Photohole Lifetimes in Ferromagnetic Gadolinium
High resolution spin-resolved photoemission is used to probe the properties
of a Gd(0001) surface state. The state shows both a spin-mixing behavior
reflecting the exchange of magnons with the local moments and a reduction of
the exchange splitting with increasing temperature. The surface state
polarization at low T suggests that the surface layer has an enhanced Tc of
365K or greater. Measurements of the photoemission linewidths show that at low
temperatures, the lifetime of a majority spin photohole is predominantly
limited by electron-phonon scattering and that of a minority spin photohole by
electron-magnon scattering. Since similar behavior may be expected for bulk
states close to the Fermi level, the transport properties of this material will
also be determined by different decay mechanisms in the two channels
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Preparation of GaAs photocathodes at low temperature
The preparation of an atomically clean surface is a necessary step in the formation of negative electron affinity (NEA) GaAs. Traditional methods to this end include cleaving, heat cleaning and epitaxial growth. Cleaving has the advantage of yielding a fresh surface after each cleave, but is limited to small areas and is not suitable for specialized structures. Heat cleaning is both simple and highly successful, so it is used as a preparation method in virtually all laboratories employing a NEA source on a regular basis. Due to its high cost and complexity, epitaxial growth of GaAs with subsequent in vacuo transfer is not a practical solution for most end users of GaAs as a NEA electron source. While simple, the heating cleaning process has a number of disadvantages. Here, a variety of cleaning techniques related to preparation of an atomically clean GaAs surface without heating to 600 C are discussed and evaluated