1,897 research outputs found
Electronic Structure and Magnetic Exchange Coupling in Ferromagnetic Full Heusler Alloys
Density-functional studies of the electronic structures and exchange
interaction parameters have been performed for a series of ferromagnetic full
Heusler alloys of general formula CoMnZ (Z = Ga, Si, Ge, Sn), RhMnZ (Z
= Ge, Sn, Pb), NiMnSn, CuMnSn and PdMnSn, and the connection
between the electronic spectra and the magnetic interactions have been studied.
Different mechanisms contributing to the exchange coupling are revealed. The
band dependence of the exchange parameters, their dependence on volume and
valence electron concentration have been thoroughly analyzed within the Green
function technique.Comment: 9 figures, 6 table
Role of covalent Fe-As bonding in the magnetic moment formation and exchange mechanisms in iron-pnictide superconductors
The electronic origin of the huge magnetostructural effect in layered Fe-As
compounds is elucidated using LiFeAs as a prototype. The crucial feature of
these materials is the strong covalent bonding between Fe and As, which tends
to suppress the exchange splitting. The bonding-antibonding splitting is very
sensitive to the distance between Fe and As nuclei. We argue that the fragile
interplay between bonding and magnetism is universal for this family of
compounds. The exchange interaction is analyzed in real space, along with its
correlation with covalency and doping. The range of interaction and itinerancy
increase as the Fe-As distance is decreased. Superexchange makes a large
antiferromagnetic contribution to the nearest-neighbor coupling, which develops
large anisotropy when the local moment is not too small. This anisotropy is
very sensitive to doping.Comment: 4+ pages, 4 color eps files; revised version accepted in Phys. Rev.
The spin angular gradient approximation in the density functional theory
A spin angular gradient approximation for the exchange correlation magnetic
field in the density functional formalism is proposed. The usage of such
corrections leads to a consistent spin dynamical approach beyond the local
approximation. The proposed technique does not contain any approximations for
the form of potential and can be used in modern full potential band structure
methods. The obtained results indicate that the direct 'potential' exchange in
3d magnets is rather small compared to the indirect 'kinetic' exchange, thus
justifies the dynamical aspect of the local density approximation in 3d metals
Long range chromomagnetic fields at high temperature
The magnetic mass of neutral gluons in Abelian chromomagnetic field at high
temperature is calculated in SU(2)$ gluodynamics. It is noted that such type
fields are spontaneously generated at high temperature. The mass is computed
either from the Schwinger-Dyson equation accounting for the one-loop
polarization tensor or in Monte-Carlo simulations on a lattice. In latter case,
an average magnetic flux penetrating a plaquette is measured for a number of
lattices. Both calculations are in agreement with each other and result in zero
magnetic mass. Some applications of the results obtained are discussed.Comment: 14 pages, 1 figur
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