50,193 research outputs found
Theory of Local Dynamical Magnetic Susceptibilities from the Korringa-Kohn-Rostoker Green Function Method
Within the framework of time-dependent density functional theory combined
with the Korringa-Kohn-Rostoker Green function formalism, we present a real
space methodology to investigate dynamical magnetic excitations from
first-principles. We set forth a scheme which enables one to deduce the correct
effective Coulomb potential needed to preserve the spin-invariance signature in
the dynamical susceptibilities, i.e. the Goldstone mode. We use our approach to
explore the spin dynamics of 3d adatoms and different dimers deposited on a
Cu(001) with emphasis on their decay to particle-hole pairs.Comment: 32 pages (preprint), 6 figures, one tabl
Gemini spectra of 12000K white dwarf stars
We report signal-to-noise ratio SNR ~ 100 optical spectra for four DA white
dwarf stars acquired with the GMOS spectrograph of the 8m Gemini north
telescope. These stars have 18<g<19 and are around Teff ~ 12000 K, were the
hydrogen lines are close to maximum. Our purpose is to test if the effective
temperatures and surface gravities derived from the relatively low
signal-to-noise ratio ( ~ 21) optical spectra acquired by the Sloan
Digital Sky Survey through model atmosphere fitting are trustworthy. Our
spectra range from 3800A to 6000A, therefore including H beta to H9. The H8
line was only marginally present in the SDSS spectra, but is crucial to
determine the gravity. When we compare the values published by Kleinman et al.
(2004) and Eisenstein et al. (2006) with our line-profile (LPT) fits, the
average differences are: Delta Teff ~ 320 K, systematically lower in SDSS, and
Delta log g ~ 0.24 dex, systematically larger in SDSS. The correlation between
gravity and effective temperature can only be broken at wavelengths bluer than
3800 A. The uncertainties in Teff are 60% larger, and in log g larger by a
factor of 4, than the Kleinman et al. (2004) and Eisenstein et al. (2006)
internal uncertainties.Comment: 11 pages and 8 figure
Spin Orbit Coupling and Spin Waves in Ultrathin Ferromagnets: The Spin Wave Rashba Effect
We present theoretical studies of the influence of spin orbit coupling on the
spin wave excitations of the Fe monolayer and bilayer on the W(110) surface.
The Dzyaloshinskii-Moriya interaction is active in such films, by virtue of the
absence of reflection symmetry in the plane of the film. When the magnetization
is in plane, this leads to a linear term in the spin wave dispersion relation
for propagation across the magnetization. The dispersion relation thus assumes
a form similar to that of an energy band of an electron trapped on a
semiconductor surfaces with Rashba coupling active. We also show SPEELS
response functions that illustrate the role of spin orbit coupling in such
measurements. In addition to the modifications of the dispersion relations for
spin waves, the presence of spin orbit coupling in the W substrate leads to a
substantial increase in the linewidth of the spin wave modes. The formalism we
have developed applies to a wide range of systems, and the particular system
explored in the numerical calculations provides us with an illustration of
phenomena which will be present in other ultrathin ferromagnet/substrate
combinations
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