169 research outputs found
Electronic structure and magnetic properties of metallocene multiple-decker sandwich nanowires
We present a study of the electronic and magnetic properties of the
multiple-decker sandwich nanowires () composed of cyclopentadienyl (CP)
rings and 3d transition metal atoms (M=Ti to Ni) using first-principles
techniques. We demonstrate using Density Functional Theory that structural
relaxation play an important role in determining the magnetic ground-state of
the system. Notably, the computed magnetic moment is zero in , while in
a significant turn-up in magnetic moment is evidenced. Two compounds
show a half-metallic ferromagnetic ground state with a gap within
minority/majority spin channel. In order to study the effect of electronic
correlations upon the half-metallic ground states in , we introduce a
simplified three-bands Hubbard model which is solved within the Variational
Cluster Approach. We discuss the results as a function of size of the reference
cluster and the strength of average Coulomb and exchange parameters.
Our results demonstrate that for the range of studied parameters and
the half-metallic character is not maintained in the presence of
local Coulomb interactions.Comment: 9 pages, 9 figures, submited to PR
Transmission through correlated CuCoCu heterostructures
The effects of local electronic interactions and finite temperatures upon the
transmission across the CuCoCu metallic heterostructure are studied in
a combined density functional and dynamical mean field theory. It is shown
that, as the electronic correlations are taken into account via a local but
dynamic self-energy, the total transmission at the Fermi level gets reduced
(predominantly in the minority spin channel), whereby the spin polarization of
the transmission increases. The latter is due to a more significant
-electrons contribution, as compared to the non-correlated case in which the
transport is dominated by and electrons.Comment: 29 pages, 7 figures, submited to PR
Absence of halfmetallicity in defect-free Cr, Mn-delta-doped Digital Magnetic Heterostructures
We present results of a combined density functional and many-body
calculations for the electronic and magnetic properties of the defect-free
digital ferromagnetic heterostructures obtained by doping GaAs with Cr and Mn.
While local density approximation/(+U) predicts half-metallicity in these
defect-free delta-doped heterostructures, we demonstrate that local many-body
correlations captured by Dynamical Mean Field Theory induce within the minority
spin channel non-quasiparticle states just above . As a consequence of the
existence of these many-body states the half-metallic gap is closed and the
carriers spin polarization is significantly reduced. Below the Fermi level the
minority spin highest valence states are found to localize more on the GaAs
layers being independent of the type of electronic correlations considered.
Thus, our results confirm the confinement of carriers in these delta-doped
heterostructures, having a spin-polarization that follow a different
temperature dependence than magnetization. We suggest that polarized
hot-electron photoluminescence experiments might bring evidence for the
existence of many-body states within the minority spin channel and their finite
temperature behavior.Comment: 10 pages 8 figures, submitted to PR
Observation and theoretical description of the pure Fano-effect in the valence-band photo-emission of ferromagnets
The pure Fano-effect in angle-integrated valence-band photo-emission of
ferromagnets has been observed for the first time. A contribution of the
intrinsic spin polarization to the spin polarization of the photo-electrons has
been avoided by an appropriate choice of the experimental parameters. The
theoretical description of the resulting spectra reveals a complete analogy to
the Fano-effect observed before for paramagnetic transition metals. While the
theoretical photo-current and spin difference spectra are found in good
quantitative agreement with experiment in the case of Fe and Co only a
qualitative agreement could be achieved in the case of Ni by calculations on
the basis of plain local spin density approximation (LSDA). Agreement with
experimental data could be improved in this case in a very substantial way by a
treatment of correlation effects on the basis of dynamical mean field theory
(DMFT).Comment: 11 pages, 3 figures accepted by PR
Magnetism and electronic structure calculation of SmN
The results of the electronic structure calculations performed on SmN by
using the LDA+U method with and without including the spin-orbit coupling are
presented. Within the LDA+U approach, a N(2) band polarization of is induced by Sm(4)-N(2) hybridization, and a half-metallic
ground state is obtained. By including spin-orbit coupling the magnetic
structure was shown to be antiferromagnetic of type II, with Sm spin and
orbital moments nearly cancelling. This results into a semiconducting ground
state, which is in agreement with experimental results.Comment: Submitted to JPCM, 12 pages, 4 figure
De Haas-van Alphen effect and Fermi surface properties of single crystal CrB2
We report the angular dependence of three distinct de Haas-van Alphen (dHvA)
frequencies of the torque magnetization in the itinerant antiferromagnet CrB2
at temperatures down to 0.3K and magnetic fields up to 14T. Comparison with the
calculated Fermi surface of nonmagnetic CrB2 suggests that two of the observed
dHvA oscillations arise from electron-like Fermi surface sheets formed by bands
with strong B-px,y character which should be rather insensitive to exchange
splitting. The measured effective masses of these Fermi surface sheets display
strong enhancements of up to a factor of two over the calculated band masses
which we attribute to electron-phonon coupling and electronic correlations. For
the temperature and field range studied, we do not observe signatures
reminiscent of the heavy d-electron bands expected for antiferromagnetic CrB2.
In view that the B-p bands are at the heart of conventional high-temperature
superconductivity in the isostructural MgB2, we consider possible implications
of our findings for nonmagnetic CrB2 and an interplay of itinerant
antiferromagnetism with superconductivity.Comment: 8 pages, 4 figure
Transmission through correlated CunCoCun heterostructures
The effects of local electronic interactions and finite temperatures upon the transmission across the Cu4CoCu4 metallic heterostructure are studied in a combined density functional and dynamical mean field theory. It is shown that, as the electronic correlations are taken into account via a local but dynamic self-energy, the total transmission at the Fermi level gets reduced (predominantly in the minority spin channel), whereby the spin polarization of the transmission increases. The latter is due to a more significant d-electrons contribution, as compared to the non-correlated case in which the transport is dominated by s and p electrons
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