178 research outputs found
Static corrections versus dynamic correlation effects in the valence band Compton profile spectra of Ni
We compute the Compton profile of Ni using the Local Density Approximation of
Density Functional Theory supplemented with electronic correlations treated at
different levels. The total/magnetic Compton profiles show not only
quantitative but also qualitative significant differences depending weather
Hubbard corrections are treated at a mean field +U or in a more sophisticated
dynamic way. Our aim is to discuss the range and capability of electronic
correlations to modify the kinetic energy along specific spatial directions.
The second and the fourth order moments of the difference in the Compton
profiles are discussed as a function of the strength of local Coulomb
interaction .Comment: 10 pages, 7 figs., submitted to PR
Trends in the magnetic properties of Fe, Co and Ni clusters and monolayers on Ir(111), Pt(111) and Au(111)
We present a detailed theoretical investigation on the magnetic properties of
small single-layered Fe, Co and Ni clusters deposited on Ir(111), Pt(111) and
Au(111). For this a fully relativistic {\em ab-initio} scheme based on density
functional theory has been used. We analyse the element, size and geometry
specific variations of the atomic magnetic moments and their mutual exchange
interactions as well as the magnetic anisotropy energy in these systems. Our
results show that the atomic spin magnetic moments in the Fe and Co clusters
decrease almost linearly with coordination on all three substrates, while the
corresponding orbital magnetic moments appear to be much more sensitive to the
local atomic environment. The isotropic exchange interaction among the cluster
atoms is always very strong for Fe and Co exceeding the values for bulk bcc Fe
and hcp Co, whereas the anisotropic Dzyaloshinski-Moriya interaction is in
general one or two orders of magnitude smaller when compared to the isotropic
one. For the magnetic properties of Ni clusters the magnetic properties can
show quite a different behaviour and we find in this case a strong tendency
towards noncollinear magnetism
Ultrafast spin polarization control of Dirac fermions in topological insulators
Three-dimensional topological insulators (TIs) are characterized by
spin-polarized Dirac-cone surface states that are protected from backscattering
by time-reversal symmetry. Control of the spin polarization of topological
surface states (TSSs) using femtosecond light pulses opens novel perspectives
for the generation and manipulation of dissipationless surface spin currents on
ultrafast timescales. Using time-, spin-, and angle-resolved spectroscopy, we
directly monitor for the first time the ultrafast response of the spin
polarization of photoexcited TSSs to circularly-polarized femtosecond pulses of
infrared light. We achieve all-optical switching of the transient out-of-plane
spin polarization, which relaxes in about 1.2 ps. Our observations establish
the feasibility of ultrafast optical control of spin-polarized Dirac fermions
in TIs and pave the way for novel optospintronic applications at ultimate
speeds.Comment: 9 pages, 4 figure
Monitoring surface resonances on Co2MnSi(100) by spin-resolved photoelectron spectroscopy
The magnitude of the spin polarization at the Fermi level of ferromagnetic
materials at room temperature is a key property for spintronics. Investigating
the Heusler compound CoMnSi a value of 93 for the spin polarization has
been observed at room temperature, where the high spin polarization is related
to a stable surface resonance in the majority band extending deep into the
bulk. In particular, we identified in our spectroscopical analysis that this
surface resonance is embedded in the bulk continuum with a strong coupling to
the majority bulk states. The resonance behaves very bulk-like, as it extends
over the first six atomic layers of the corresponding (001)-surface. Our study
includes experimental investigations, where the bulk electronic structure as
well as surface-related features have been investigated using spin-resolved
photoelectron spectroscopy (SR-UPS) and for a larger probing depth
spin-integrated high energy x-ray photoemission spectroscopy (HAXPES). The
results are interpreted in comparison with first-principles band structure and
photoemission calculations which consider all relativistic, surface and
high-energy effects properly.Comment: 9 pages, 8 figures, Heusler alloy, electronic structure and
photoemissio
- …