  Multiple-band electronic structure and proximity to antiferromagnetic (AF)
instability are the key properties of iron-based superconductors. We explore
the influence of scattering by the AF spin fluctuations on transport of
multiple-band metals above the magnetic transition. A salient feature of
scattering on the AF fluctuations is that it is strongly enhanced at the Fermi
surface locations where the nesting is perfect ("hot spots" or "hot lines"). We
review derivation of the collision integral for the Boltzmann equation due to
AF-fluctuations scattering. In the paramagnetic state, the enhanced scattering
rate near the hot lines leads to anomalous behavior of electronic transport in
magnetic field. We explore this behavior by analytically solving Boltzmann
transport equation with approximate transition rates. This approach accounts
for return scattering events and is more accurate than the relaxation-time
approximation. The magnetic-field dependences are characterized by two very
different field scales, the lower scale is set by the hot-spot width and the
higher scale is set by the total scattering amplitude. A conventional
magnetotransport behavior is limited to magnetic fields below the lower scale.
In the wide range in between these two scales the longitudinal conductivity has
linear dependence on the magnetic field and the Hall conductivity has quadratic
dependence. The linear dependence of the diagonal component reflects growth of
the Fermi-surface area affected by hot spots proportional to the magnetic
field. We discuss applicability of this theoretical framework for describing of
anomalous magnetotransport properties in different iron pnictides and selenides
in the paramagnetic state.
