109 research outputs found
Topological insulators and thermoelectric materials
Topological insulators (TIs) are a new quantum state of matter which have
gapless surface states inside the bulk energy gap. Starting with the discovery
of two dimensional TIs, the HgTe-based quantum wells, many new topological
materials have been theoretically predicted and experimentally observed.
Currently known TI materials can possibly be classified into two families, the
HgTe family and the Bi2Se family. The signatures found in the electronic
structure of a TI also cause these materials to be excellent thermoelectric
materials. On the other hand, excellent thermoelectric materials can be also
topologically trivial. Here we present a short introduction to topological
insulators and thermoelectrics, and give examples of compound classes were both
good thermoelectric properties and topological insulators can be found.Comment: Phys. Status Solidi RRL, accepte
Half-metallic ferromagnetism with high magnetic moment and high Curie temperature in CoFeSi
CoFeSi crystallizes in the ordered L2 structure as proved by X-ray
diffraction and M\"o\ss bauer spectroscopy. The magnetic moment of CoFeSi
was measured to be about at 5K. Magnetic circular dichroism spectra
excited by soft X-rays (XMCD) were taken to determine the element specific
magnetic moments of Co and Fe. The Curie temperature was measured with
different methods to be ()K. CoFeSi was found to be the Heusler
compound as well as the half-metallic ferromagnet with the highest magnetic
moment and Curie temperature.Comment: conference contribution, MMM200
Systematical, experimental investigations on LiMgZ (Z= P, As, Sb) wide band gap semiconductors
This work reports on the experimental investigation of the wide band gap
compounds LiMgZ (Z = P, As, Sb), which are promising candidates for
opto-electronics and anode materials for Lithium batteries. The compounds
crystallize in the cubic (C1_b) MgAgAs structure (space group F-43m). The
polycrystalline samples were synthesized by solid state reaction methods. X-ray
and neutron diffraction measurements show a homogeneous, single-phased samples.
The electronic properties were studied using the direct current (DC) method.
Additionally UV-VIS diffuse reflectance spectra were recorded in order to
investigate the band gap nature. The measurements show that all compounds
exhibit semiconducting behavior with direct band gaps of 1.0 eV to 2.3 eV
depending on the Z element. A decrease of the peak widths in the static 7Li
nuclear magnetic resonance (NMR) spectra with increasing temperature was
observed, which can directly be related to an increase of Li ion mobility.Comment: 8 page
Giant magnetoresistance and extraordinary magnetoresistance in inhomogeneous semiconducting DyNiBi
The semiconducting half-Heulser compound DyNiBi shows a negative giant
magnetoresistance (GMR) below 200 K. Except for a weak deviation, this
magnetoresistance scales roughly with the square of the magnetization in the
paramagnetic state, and is related to the metal-insulator transition. At low
temperature, a positive magnetoresistance is found, which can be suppressed by
high fields. The magnitude of the positive magnetoresistance changes slightly
with the amount of impurity phase.Comment: 3 pages, 3 figure
Searching for hexagonal analogues of the half-metallic half-Heusler XYZ compounds
The XYZ half-Heusler crystal structure can conveniently be described as a
tetrahedral zinc blende YZ structure which is stuffed by a slightly ionic X
species. This description is well suited to understand the electronic structure
of semiconducting 8-electron compounds such as LiAlSi (formulated
Li[AlSi]) or semiconducting 18-electron compounds such as TiCoSb
(formulated Ti[CoSb]). The basis for this is that [AlSi]
(with the same electron count as Si) and [CoSb] (the same electron
count as GaSb), are both structurally and electronically, zinc-blende
semiconductors. The electronic structure of half-metallic ferromagnets in this
structure type can then be described as semiconductors with stuffing magnetic
ions which have a local moment: For example, 22 electron MnNiSb can be written
Mn[NiSb]. The tendency in the 18 electron compound for a
semiconducting gap -- believed to arise from strong covalency -- is carried
over in MnNiSb to a tendency for a gap in one spin direction. Here we similarly
propose the systematic examination of 18-electron hexagonal compounds for
semiconducting gaps; these would be the "stuffed wurtzite" analogues of the
"stuffed zinc blende" half-Heusler compounds. These semiconductors could then
serve as the basis for possibly new families of half-metallic compounds,
attained through appropriate replacement of non-magnetic ions by magnetic ones.
These semiconductors and semimetals with tunable charge carrier concentrations
could also be interesting in the context of magnetoresistive and thermoelectric
materials.Comment: 11 pages, 6 figures, of which 4 are colou
Manure from cattle as fertilizer for soil fertility and growth characteristics of Tall Fescue (Festuca arundinacea) and Smuts Finger grass (Digitaria eriantha)
Applying cattle manure to soil in optimum rates can enhance soil fertility and plant growth. The objectives of this study were to investigate the influence of different rates of cattle manure application on soil fertility and the growth and productivity of Tall Fescue (Festuca arundinaceae) and Smuts Finger grass (Digitaria eriantha), two popular pasture species in South Africa. These field trials were established on a uniform sandy clay loam (Hutton) soil on the Hatfield Experimental Farm, of the University of Pretoria in Pretoria. There were five treatments comprising five rates of cattle manure incorporation (0, 20, 40, 80 and 120 tonnes/ha). During the growing season, Tall Fescue plants from cattle manure-amended plots were significantly taller in the 80 tonnes/ha treatment, while Smuts Finger grass reached the maximum height in the 40 tonnes/ha treatment.Coaltech 2020http://www.lrrd.orghb201
entos: A Quantum Molecular Simulation Package
entos is designed for ab initio MD simulations of molecular and condensed-phase chemical reactions and other processes, with particular focus on mean-field and quantum embedding methods for electronic structure. The entos software package is developed in the C++14 programming language with a structure that enables
flexibility (by providing a long-term sustainable platform for development of methods in this area), efficiency (via task-based multi-threaded parallelism), and rigorous software engineering standards
entos: A Quantum Molecular Simulation Package
entos is designed for ab initio MD simulations of molecular and condensed-phase chemical reactions and other processes, with particular focus on mean-field and quantum embedding methods for electronic structure. The entos software package is developed in the C++14 programming language with a structure that enables
flexibility (by providing a long-term sustainable platform for development of methods in this area), efficiency (via task-based multi-threaded parallelism), and rigorous software engineering standards
Childhood in Sociology and Society: The US Perspective
The field of childhood studies in the US is comprised of cross-disciplinary researchers who theorize and conduct research on both children and youth. US sociologists who study childhood largely draw on the childhood literature published in English. This article focuses on American sociological contributions, but notes relevant contributions from non-American scholars published in English that have shaped and fueled American research. This article also profiles the institutional support of childhood research in the US, specifically outlining the activities of the ‘Children and Youth’ Section of the American Sociological Association (ASA), and assesses the contributions of this area of study for sociology as well as the implications for an interdisciplinary field.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
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