Search results for "NGS"
showing 10 items of 6306 documents
Magnetic properties of Co2Mn1−xFexSi Heusler alloys
2006
Co2Mn1−xFexSi Heusler alloys with Fe concentration x = 0–0.4 as prepared by arc melting show a L21 long range order for all Fe concentrations. Magnetic properties of Co2Mn1−xFexSi Heusler alloys were investigated by magnetometry and circular magnetic dichroism. The magnetization of the Fe doped Heusler alloys is in agreement with the Slater–Pauling values expected for half-metallic ferromagnets. Element specific magnetic moments as determined by x-ray absorption using the total electron yield method are in disagreement with theoretical predictions for x = 0 but approach the predicted values as the Fe concentration increases. Surprisingly small Fe concentration increases the magnetic moments…
High-spin polarization of Heusler alloys
2006
Fermi surface of a half-metal compound with cubic Fm–3m symmetry: Heusler alloy or double perovskite.The inset shows the spin resolved density of state for a CCFA Heusler compound. ( This illustration appears on the cover of the print edition. ) This cluster issue of Journal of Physics D: Applied Physics is devoted to magnetic Heusler alloys. This class of materials is currently considered to contain the most attractive half-metallic ferromagnets due to their high Curie temperatures and their structural relation to conventional semiconductors. The first compound to be identified as a half-metallic ferromagnet, by de Groot et al back in 1983, was the half-Heusler alloy NiMnSb. After a period…
Effects of post-growth annealing on structural and compositional properties of the Co2Cr0.6Fe0.4Al surface and its relevance for the surface electron…
2009
In this study we investigate the influence of post-growth annealing on different Co2Cr0.6Fe0.4Al samples. We find strong changes in the geometric surface structure as well as in the element specific concentrations during the annealing process. These irreversible changes go in hand with characteristic changes in the electron spin polarization (ESP) at the surface: as observed in Cinchetti et al (2007 J. Phys. D: Appl. Phys. 40 1544), the iron buffered sample shows the largest spin polarization at the Fermi level. The latter remains positive as a consequence of the reduced density of states for the minority carriers due to the predicted minority gap, which can be clearly seen for all samples …
A spatially resolved investigation of the local, micro-magnetic domain structure of single and polycrystalline Co2FeSi
2007
The Heusler compound Co2FeSi is a promising material for magneto-electronic devices. With a Curie temperature of 1100?K and a saturation magnetization of 6?Bohr magnetons and a high spin polarization at the Fermi edge it fulfils the essential requirements for magnetic sensors or spin valve structures. An essential feature for such devices is the micro-magnetic domain structure. X-ray magnetic circular dichroism?photo emission electron microscopy has been used for a direct observation of the domain structure of single- and polycrystalline samples. The polycrystalline material exhibits a micro-magnetic ripple structure, as it is well known for pure Co and other polycrystalline Heusler compoun…
Exchange stiffness in the Co2FeSi Heusler compound
2009
Using Brillouin light scattering spectroscopy, we determine the spin-wave exchange stiffness D and the exchange constant A for thin films of the full Heusler compound Co2FeSi prepared by pulsed laser deposition. The thermal spin-wave spectra were measured in various magnetic fields, for different transferred spin-wave momenta, and for different film thicknesses. Fitting the observed spin-wave frequencies, we find an extraordinarily large value of
Incorporation of Li dopant into Cu2ZnSnSe4 photovoltaic absorber: hybrid-functional calculations
2015
We have studied the formation of Li extrinsic defects in CuZnSnSe by first-principles hybrid functional calculations. Li atoms in the Cu site (Li) and Li atoms in the Se site (Li) are the most and the least stable point defect, respectively. The formation energies of two Li interstitial defects with different numbers of nearest neighbors are the same. These interstitial point defects act as a donor but do not create gap states. Formation of the acceptor point defects (Li and Li) is less likely in p-type CuZnSnSe compared with n-type CuZnSnSe. In contrast to Li which does not create gap states, the formation of Li creates two charge transition levels in the middle of the bandgap which might …
Off-stoichiometry in Co2FeSi thin films sputtered from stoichiometric targets revealed by nuclear magnetic resonance
2009
Co2FeSi is predicted to be a half-metallic ferromagnet with an extraordinary high magnetic moment and Curie temperature. However, a low tunnel magneto-resistance ratio, a lower spin polarization and a lower magnetic moment were experimentally observed in thin film samples. Consequently, thin Co2FeSi films of different groups were studied using spin-echo nuclear magnetic resonance (NMR). NMR probes the local hyperfine fields of the active atoms, which strongly depend on the local environment. NMR is thus able to reveal the next neighbouring shells of the Co-59 nuclei in the Co2FeSi thin films. As expected, our NMR study shows the main resonance line corresponding to Co-59 nuclei in the L2(1)…
Modelling infiltration by means of a nonlinear fractional diffusion model
2006
The classical Richards equation describes infiltration into porous soil as a nonlinear diffusion process. Recent experiments have suggested that this process exhibits anomalous scaling behaviour. These observations suggest generalizing the classical Richards equation by introducing fractional time derivatives. The resulting fractional Richards equation with appropriate initial and boundary values is solved numerically in this paper. The numerical code is tested against analytical solutions in the linear case. Saturation profiles are calculated for the fully nonlinear fractional Richards equation. Isochrones and isosaturation curves are given. The cumulative moisture intake is found as a fun…
The 2020 magnetism roadmap
2020
Following the success and relevance of the 2014 and 2017 Magnetism Roadmap articles, this 2020 Magnetism Roadmap edition takes yet another timely look at newly relevant and highly active areas in magnetism research. The overall layout of this article is unchanged, given that it has proved the most appropriate way to convey the most relevant aspects of today's magnetism research in a wide variety of sub-fields to a broad readership. A different group of experts has again been selected for this article, representing both the breadth of new research areas, and the desire to incorporate different voices and viewpoints. The latter is especially relevant for thistype of article, in which one's fi…
Optical properties of silver halide fibres: ageing effects
1996
The relation between the structure of fibres extruded from mixed silver halides and their IR optical losses and luminescence properties is studied. The recently established ageing effect of the considerable growth of mean grain size of the fibre's polycrystalline structure (typically from 20 to 1000 nm in two years) is correlated with IR and luminescence measurements. IR spectra measured in the interval show growth of the concentrations of molecular impurities. The luminescence measurements are used for the characterization of the fibre's structure ordering. The luminescence decay kinetics is analysed theoretically in terms of the diffusion-controlled recombination of spatially well-correla…