3 research outputs found
Interplay between magnetic properties and Fermi surface nesting in iron pnictides
The wave-vector q and doping (x,y) dependences of the magnetic energy, iron
moment, and effective exchange interactions in LaFeAsO{1-x}F{x} and
Ba{1-2y}K{2y}Fe2As2 are studied by self-consistent LSDA calculations for
co-planar spin spirals. For the undoped compounds (x=0, y=0), the minimum of
the calculated total energy, E(q), is for q corresponding to stripe
antiferromagnetic order. Already at low levels of electron doping (x), this
minimum becomes flat in LaFeAsO{1-x}F{x} and for x>=5, it shifts to an
incommensurate q. In Ba{1-2y}K{2y}Fe2As2, stripe order remains stable for hole
doping up to y=0.3. These results are explained in terms of the band structure.
The magnetic interactions cannot be accurately described by a simple classical
Heisenberg model and the effective exchange interactions fitted to E(q) depend
strongly on doping. The doping dependence of the E(q) curves is compared with
that of the noninteracting magnetic susceptibility for which similar trends are
found.Comment: 17 pages, 5 figure
Temperature-dependent striped antiferromagnetism of LaFeAsO in a Green's function approach
We use a Green's function method to study the temperature-dependent average
moment and magnetic phase-transition temperature of the striped
antiferromagnetism of LaFeAsO, and other similar compounds, as the parents of
FeAs-based superconductors. We consider the nearest and the next-nearest
couplings in the FeAs layer, and the nearest coupling for inter-layer spin
interaction. The dependence of the transition temperature TN and the
zero-temperature average spin on the interaction constants is investigated. We
obtain an analytical expression for TN and determine our temperature-dependent
average spin from zero temperature to TN in terms of unified self-consistent
equations. For LaFeAsO, we obtain a reasonable estimation of the coupling
interactions with the experimental transition temperature TN = 138 K. Our
results also show that a non-zero antiferromagnetic (AFM) inter-layer coupling
is essential for the existence of a non-zero TN, and the many-body AFM
fluctuations reduce substantially the low-temperature magnetic moment per Fe
towards the experimental value. Our Green's function approach can be used for
other FeAs-based parent compounds and these results should be useful to
understand the physical properties of FeAs-based superconductors.Comment: 12 page