50 research outputs found
Intrinsic anomalous Hall effect in nickel: An GGA+U study
The electronic structure and intrinsic anomalous Hall conductivity of nickel
have been calculated based on the generalized gradient approximation (GGA) plus
on-site Coulomb interaction (GGA+U) scheme. It is found that the intrinsic
anomalous Hall conductivity () obtained from the GGA+U
calculations with eV and eV, is in nearly perfect agreement
with that measured recently at low temperatures while, in contrast, the
from the GGA calculations is about 100% larger than the
measured one. This indicates that, as for the other spin-orbit interaction
(SOI)-induced phenomena in 3 itinerant magnets such as the orbital magnetic
magnetization and magnetocrystalline anisotropy, the on-site electron-electron
correlation, though moderate only, should be taken into account properly in
order to get the correct anomalous Hall conductivity. The intrinsic
and the number of valence electrons () have also been
calculated as a function of the Fermi energy (). A sign change is
predicted at eV (), and this explain qualitatively
why the theoretical and experimental values for Fe and Co are
positive. It is also predicted that fcc NiCo(Fe,Cu) alloys with
being small, would also have the negative with the
magnitude being in the range of cm. The most
pronounced effect of including the on-site Coulomb interaction is that all the
-dominant bands are lowered in energy relative to the by about 0.3 eV,
and consequently, the small minority spin X hole pocket disappears. The
presence of the small X hole pocket in the GGA calculations is attributed
to be responsible for the large discrepancy in the between
theory and experiment.Comment: 7 pages, 3 figures; Accepted for publication in Physical Review
Spatially resolved observation of uniform precession modes in spin-valve systems
Using time-resolved photoemission electron microscopy the excitation of
uniform precession modes in individual domains of a weakly coupled spin-valve
system has been studied. A coupling dependence of the precession frequencies
has been found that can be reasonably well understood on the basis of a
macrospin model. By tuning the frequency of the excitation source the uniform
precession modes are excited in a resonant way.Comment: This article has been accepted by Journal of Applied Physics. After
it is published, it will be found at http://jap.aip.or
Electronic structure and effects of dynamical electron correlation in ferromagnetic bcc-Fe, fcc-Ni and antiferromagnetic NiO
LDA+DMFT method in the framework of the iterative perturbation theory (IPT)
with full LDA Hamiltonian without mapping onto the effective Wannier orbitals.
We then apply this LDA+DMFT method to ferromagnetic bcc-Fe and fcc-Ni as a test
of transition metal, and to antiferromagnetic NiO as an example of transition
metal oxide. In Fe and Ni, the width of occupied 3d bands is narrower than
those in LDA and Ni 6eV satellite appears. In NiO, the resultant electronic
structure is of charge-transfer insulator type and the band gap is 4.3eV. These
results are in good agreement with the experimental XPS. The configuration
mixing and dynamical correlation effects play a crucial role in these results
Orbital contribution to the magnetic properties of iron as a function of dimensionality
The orbital contribution to the magnetic properties of Fe in systems of
decreasing dimensionality (bulk, surfaces, wire and free clusters) is
investigated using a tight-binding hamiltonian in an and atomic
orbital basis set including spin-orbit coupling and intra-atomic electronic
interactions in the full Hartree-Fock (HF) scheme, i.e., involving all the
matrix elements of the Coulomb interaction with their exact orbital dependence.
Spin and orbital magnetic moments and the magnetocrystalline anisotropy energy
(MAE) are calculated for several orientations of the magnetization. The results
are systematically compared with those of simplified hamiltonians which give
results close to those obtained from the local spin density approximation. The
full HF decoupling leads to much larger orbital moments and MAE which can reach
values as large as 1 and several tens of meV, respectively, in the
monatomic wire at the equilibrium distance. The reliability of the results
obtained by adding the so-called Orbital Polarization Ansatz (OPA) to the
simplified hamiltonians is also discussed. It is found that when the spin
magnetization is saturated the OPA results for the orbital moment are in
qualitative agreement with those of the full HF model. However there are large
discrepancies for the MAE, especially in clusters. Thus the full HF scheme must
be used to investigate the orbital magnetism and MAE of low dimensional
systems
Experimental application of sum rules for electron energy loss magnetic chiral dichroism
We present a derivation of the orbital and spin sum rules for magnetic
circular dichroic spectra measured by electron energy loss spectroscopy in a
transmission electron microscope. These sum rules are obtained from the
differential cross section calculated for symmetric positions in the
diffraction pattern. Orbital and spin magnetic moments are expressed explicitly
in terms of experimental spectra and dynamical diffraction coefficients. We
estimate the ratio of spin to orbital magnetic moments and discuss first
experimental results for the Fe L_{2,3} edge.Comment: 11 pages, 2 figure
Interaction of magnetization and heat dynamics for pulsed domain wall movement with Joule heating
Pulsed domain wall movement is studied here in Ni80Fe20 nanowires on SiO2, using a fully integrated electrostatic, thermoelectric, and micromagnetics solver based on the Landau-Lifshitz- Bloch equation, including Joule heating, anisotropic magneto-resistance, and Oersted field contributions.
During the applied pulse, the anisotropic magneto-resistance of the domain wall generates a dynamic heat gradient, which increases the current-driven velocity by up to 15%. Using a temperature-dependent conductivity, significant differences are found between the constant voltage-pulsed and constant current-pulsed domain wall movement: constant voltage pulses are
shown to be more efficient at displacing domain walls whilst minimizing the increase in temperature,
with the total domain wall displacement achieved over a fixed pulse duration having a maximum with respect to the driving pulse strength
Development of Improved Methods for Low Template DNA Analysis
We investigated on the crystallographic, morphological and magnetic characteristics of barium ferrite-SiO2/Si films prepared by sol-gel dip coating method. It is found that the sol obtained at 80°C for 90 min. is the most suitable for coating. The particles formed in the films prepared by heat treatment at 800°C for 3 hours exhibits needle-like particles placing parallel to substrate. The saturation magnetization increases as thickness increases, and its maximum value is 260 emu/cm3. The direction of easy-magnetization in the films has tendency to vary from perpendicular to parallel to substrate as thickness increases
Hochtemperaturreaktor zur Meerwasserentsalzung
Es werden Anlagen zur Meerwasserentsalzung mit Hilfe von HTR diskutiert. Wirtschaftliche Aspekte einer Zweizweckanlage mit Hochtemperaturreaktor als Wärmequelle, Gasturbine als Elektrizitätserzeuger und Entsalzung nach dem MSF-Verfahren werden untersucht und mit Einzweckanlagen verglichen. Es wurde ein Programm aufgestellt zur Berechnung von Kapital-, Brennstoff- und Betriebskosten einer solchen Anlage. Als Ergebnis dieser Untersuchungen kann hervorgehoben werden, daß ein kostengünstiger Einsatz der Gasturbine-MSF-Mehrzweckanlage bis zu einem Verhältnis von 15 kg/kWh Wasserherstellung zu Stromerzeugung je nach Kapazitätmöglich ist - verglichen mit Werten bis 160 kg/kWh bei Dampfprozessen