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.