2 research outputs found
Antiferromagnetic order in multi-band Hubbard models for iron-pnictides
We investigate multi-band Hubbard models for the three iron 3-
bands and the two iron 3- bands in by means of the
Gutzwiller variational theory. Our analysis of the paramagnetic ground state
shows that neither Hartree--Fock mean-field theories nor effective spin models
describe these systems adequately. In contrast to Hartree--Fock-type
approaches, the Gutzwiller theory predicts that antiferromagnetic order
requires substantial values of the local Hund's-rule exchange interaction. For
the three-band model, the antiferromagnetic moment fits experimental data for a
broad range of interaction parameters. However, for the more appropriate
five-band model, the iron electrons polarize the electrons and
they substantially contribute to the ordered moment.Comment: 4 pages, 4 figure
Magnetic order in orbital models of the iron pnictides
We examine the appearance of the experimentally-observed stripe
spin-density-wave magnetic order in five different orbital models of the iron
pnictide parent compounds. A restricted mean-field ansatz is used to determine
the magnetic phase diagram of each model. Using the random phase approximation,
we then check this phase diagram by evaluating the static spin susceptibility
in the paramagnetic state close to the mean-field phase boundaries. The momenta
for which the susceptibility is peaked indicate in an unbiased way the actual
ordering vector of the nearby mean-field state. The dominant orbitally resolved
contributions to the spin susceptibility are also examined to determine the
origin of the magnetic instability. We find that the observed stripe magnetic
order is possible in four of the models, but it is extremely sensitive to the
degree of the nesting between the electron and hole Fermi pockets. In the more
realistic five-orbital models, this order competes with a strong-coupling
incommensurate state which appears to be controlled by details of the
electronic structure below the Fermi energy. We conclude by discussing the
implications of our work for the origin of the magnetic order in the pnictides.Comment: 19 pages, 19 figures; published version, typos corrected, references
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