1,173 research outputs found
Mapping the magnetic exchange interactions from first principles: Anisotropy anomaly and application to Fe, Ni, and Co
Mapping the magnetic exchange interactions from model Hamiltonian to density
functional theory is a crucial step in multi-scale modeling calculations.
Considering the usual magnetic force theorem but with arbitrary rotational
angles of the spin moments, a spurious anisotropy in the standard mapping
procedure is shown to occur provided by bilinear-like contributions of high
order spin interactions. The evaluation of this anisotropy gives a hint on the
strength of non-bilinear terms characterizing the system under investigation.Comment: 11 pages, 1 figur
Multilayers of Zinc-Blende Half-Metals with Semiconductors
We report on first-principles calculations of multilayers of zinc-blende
half-metallic ferromagnets CrAs and CrSb with III-V and II-VI semiconductors,
in the [001] orientation. We examine the ideal and tetragonalised structures,
as well as the case of an intermixed interface. We find that, as a rule,
half-metallicity can be conserved throughout the heterostructures, provided
that the character of the local coordination and bonding is not disturbed. At
the interfaces with semiconductors, we describe a mechanism that can give also
a non-integer spin moment per interface transition atom, and derive a simple
rule to evaluate it
Ballistic Spin Injection and Detection in Fe/Semiconductor/Fe Junctions
We present {\it ab initio} calculations of the spin-dependent electronic
transport in Fe/GaAs/Fe and Fe/ZnSe/Fe (001) junctions simulating the situation
of a spin-injection experiment. We follow a ballistic Landauer-B\"uttiker
approach for the calculation of the spin-dependent dc conductance in the
linear-responce regime, in the limit of zero temperature. We show that the bulk
band structure of the leads and of the semiconductor, and even more the
electronic structure of a clean and abrupt interface, are responsible for a
current polarisation and a magnetoresistance ratio of almost the ideal 100%, if
the transport is ballistic. In particular we study the significance of the
transmission resonances caused by the presence of two interfaces.Comment: 13 pages, 9 figure
Flamelet modelling of soot formation in diffusion flames
In this work the steady and unsteady flamelet models have been applied to soot formation in laminar and turbulent diffusion flames. The aim was to study how different model parameters affect soot formation in diffusion flames. It was shown that certain assumptions are more crucial in laminar diffusion flames than in turbulent ones. The soot formation in turbulent diffusion flames is more sensitive to the surface dependence of the particle and altering the active site parameter, than in laminar flames. This is due to the fact that the flame is laminar and the turbulent mixing, which supplies the particle with radicals, does not affect the process. The active site parameter decreases in the absence of radicals. The modelling of complex diffusivity of all species is more relevant in laminar diffusion flames than in turbulent diffusion flames. All transient effects investigated in this work were shown to affect soot formation, which is itself transient. It was shown that these effects are more relevant for laminar fames than for turbulent flames. The steady flamelet model allows the inclusion of many transient processes and thereby loses in accuracy compared with the unsteady model. Finally, the process of the formation of agglomerates was included in the unsteady model and it was shown that the soot volume fraction is affected when this process is considered
The combined effect of temperature and disorder on interlayer exchange coupling in magnetic multilayers
We study the combined effect of temperature and disorder in the spacer on the
interlayer exchange coupling. The temperature dependence is treated on ab
initio level. We employ the spin-polarized surface Green function technique
within the tight-binding linear muffin-tin orbital method and the Lloyd
formulation of the IEC. The integrals involving the Fermi-Dirac distribution
are calculated using an efficient method based on representation of integrands
by a sum of complex exponentials. Application is made to
Co/Cu_{100-x}M_x/Co(001) trilayers (M=Zn, Au, and Ni) with varying thicknesses
of the spacer.Comment: 5 pages, LaTeX, 1 figure. Submitted to Phil. Mag.
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