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Abstract
We review the electronic and magnetic properties of the quinternary full Heusler alloys
of the type Co\(_2\)[Cr\(_{1-x}\)Mn\(_x\)][Al\(_{1-y}\)Si\(_y\)] 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 \(sp\) 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.