  The experimentally observed bad metal behavior in parent iron pnictides and
chalcogenides suggests that these systems contain strong electronic
correlations and are on the verge of a metal-to-insulator transition. The
magnetic excitations in this bad-metal regime mainly derive from the incoherent
part of the electronic spectrum away from the Fermi energy. We present a
microscopic study of the exchange interactions in such a regime within a slave
rotor approach. We find that the exchange interaction is maximized near the
Mott transition. Generalizations to the multi-orbital case are discussed, as
are the implications for the strength of superconducting pairing amplitude in
the iron-based superconductors.
