476 research outputs found
Spin-polarization and electronic properties of half-metallic Heusler alloys calculated from first-principles
Half-metallic Heusler alloys are amongst the most promising materials for
future magnetoelectronic applications. We review some recent results on the
electronic properties of these compounds. The origin of the gap in these
half-metallic alloys and its connection to the magnetic properties are well
understood. Changing the lattice parameter shifts slightly the Fermi level.
Spin-orbit coupling induces states within the gap but the alloys keep a very
high degree of spin-polarization at the Fermi level. Small degrees of doping
and disorder as well as defects with low formation energy have little effect on
the properties of the gap, while temperature effects can lead to a quick loss
of half-metallicity. Finally we discuss two special issues; the case of
quaternary Heusler alloys and the half-metallic ferrimagnets
Engineering the electronic, magnetic and gap-related properties of the quinternary half-metallic Heusler alloys
We review the electronic and magnetic properties of the quinternary full
Heusler alloys of the type Co[CrMn][AlSi] employing
three different approaches : (i) the coherent potential approximation (CPA),
(ii) the virtual crystal approximation (VCA), and (iii) supercell calculations
(SC). All three methods give similar results and the local environment
manifested itself only for small details of the density of states. All alloys
under study are shown to be half-metals and their total spin moments follow the
so-called Slater-Pauling behavior of the ideal half-metallic systems. We
especially concentrate on the properties related to the minority-spin band-gap.
We present the possibility to engineer the properties of these alloys by
changing the relative concentrations of the low-valent transition metal and
atoms in a continuous way. Our results show that for realistic
applications, ideal are the compounds rich in Si and Cr since they combine
large energy gaps (around 0.6 eV), robust half-metallicity with respect to
defects (the Fermi level is located near the middle of the gap) and high values
of the majority-spin density of states around the Fermi level which are needed
for large values of the perfectly spin-polarized current in spintronic devices
like spin-valves or magnetic tunnel junctions.Comment: 17 pages, 10 figure
Role of defects and disorder in the half-metallic full-Heusler compounds
Half-metallic ferromagnets and especially the full-Heusler alloys containing
Co are at the center of scientific research due to their potential applications
in spintronics. For realistic devices it is important to control accurately the
creation of defects in these alloys. We review some of our late results on the
role of defects and impurities in these compounds. More precisely we present
results for the following cases (i) doping and disorder in CoCr(Mn)Al(Si)
alloys, (ii) half-metallic ferrimagnetism appeared due to the creation of
Cr(Mn) antisites in these alloys, (iii) Co-doping in MnVAl(Si) alloys
leading to half-metallic antiferromagnetism, and finally (iv) the occurrence of
vacancies in the full-Heusler alloys containing Co and Mn. These results are
susceptible of encouraging further theoretical and experimental research in the
properties of these compounds.Comment: Chapter intended for a book with contributions of the invited
speakers of the International Conference on Nanoscale Magnetism 2007. Revised
version contains new figure
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